Pasados seminarios
Local and non-local models of quantum gravity
Ponente: Ilya L. Shapiro
Filiación: Universidade Federal de Juiz de Fora
Resumen: The main difficulty of perturbative quantum gravity (QG) in D=4 dimensions is the conflict between renormalizability and unitarity of the theory. The simplest version of QG is based on General Relativity and turns out to be nonrenormalizable. One can construct renormalizable and even superrenormalizable versions of QG by introducing higher derivatives. In the local versions of higher derivative models of QG there are always unphysical higherderivative massive unphysical ghosts. One can construct non-polynomial in derivatives (or, equivalently, nonlocal) models of QG, which have no ghosts at the tree level. However, taking loop corrections into account one meets infinite amount of ghost-like complex states. The theories of both local and nonlocal types attracted a lot of attention in the last years and our purpose it to present a brief review of the problems and perspectives of these models, according to the present-day understanding.
Resumen: The main difficulty of perturbative quantum gravity (QG) in D=4 dimensions is the conflict between renormalizability and unitarity of the theory. The simplest version of QG is based on General Relativity and turns out to be nonrenormalizable. One can construct renormalizable and even superrenormalizable versions of QG by introducing higher derivatives. In the local versions of higher derivative models of QG there are always unphysical higherderivative massive unphysical ghosts. One can construct non-polynomial in derivatives (or, equivalently, nonlocal) models of QG, which have no ghosts at the tree level. However, taking loop corrections into account one meets infinite amount of ghost-like complex states. The theories of both local and nonlocal types attracted a lot of attention in the last years and our purpose it to present a brief review of the problems and perspectives of these models, according to the present-day understanding.
Fecha
y hora: 24 de febrero de 2020,
15:00 h.
Stringy corrections to supergravity black holes
Ponente: Tomás Ortín
Filiación: IFT - CSIC/UAM
Resumen: At low energies, the dynamics of string theoreis can be approximated quite well by an effective theory of the fields that describe the massless excitations of the string, which always includes a graviton. The effective field theory admits a double expansion in the string coupling constant and in the string length (squared). At lowest order in the string length the string theory effective action is just an ordinary theory of (super)gravity coupled to some amssless fields. Terms of higher order in the string length in the action are of higher order in curvatures. They represent genuine stringy effects that correct the lowest-order behavior. they are very interesting, but very difficult to compute. In this talk I will review the basics of the string effective action and its first stringy corrections for the particular case of the heterotic superstring. I will then consider several solutions of the lowest-order action that correspond to several kinds of black holes, including the non-extremal Reissner-Nordstrom one and I will show how to compute their first stringy corrections and the corrections to their Q/M ratios in the extremal limit (relevant in the context of the Weak Gravity Conjecture), temperatures and entropies using Wald's formalism.
Resumen: At low energies, the dynamics of string theoreis can be approximated quite well by an effective theory of the fields that describe the massless excitations of the string, which always includes a graviton. The effective field theory admits a double expansion in the string coupling constant and in the string length (squared). At lowest order in the string length the string theory effective action is just an ordinary theory of (super)gravity coupled to some amssless fields. Terms of higher order in the string length in the action are of higher order in curvatures. They represent genuine stringy effects that correct the lowest-order behavior. they are very interesting, but very difficult to compute. In this talk I will review the basics of the string effective action and its first stringy corrections for the particular case of the heterotic superstring. I will then consider several solutions of the lowest-order action that correspond to several kinds of black holes, including the non-extremal Reissner-Nordstrom one and I will show how to compute their first stringy corrections and the corrections to their Q/M ratios in the extremal limit (relevant in the context of the Weak Gravity Conjecture), temperatures and entropies using Wald's formalism.
Fecha
y hora: 27 de enero de 2020,
15:00 h.
Lugar: CSIC, CFMAC, sala de
conferencias (Serrano,
121)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (3.ª planta)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2.ª planta)
Fricción cuántica y fuerzas de Casimir entre detectores de Unruh-deWitt y placas
Ponente: Pablo Rodríguez López
Filiación: URJC
Resumen: En esta charla vamos a ver cómo usar Teoría de Campos y el formalismo de Scattering para estudiar diversos fenómenos físicos cuyo origen es la naturaleza cuántico-fluctuante del campo electromagnético (junto con la ruptura de simetrías translacionales y/o el no equilibrio termodinámico), como las fuerzas de Casimir y la emisibilidad y transferencia de calor entre cuerpos. En particular, tras una introducción teórica, me voy a centrar en el efecto Casimir y la trasferencia de calor entre materiales 2D de la familia del grafeno (con lo que veremos la importancia de la dimensionalidad y las propiedades de las respuestas electromagnéticas de los materiales) y, con un tratamiento relativista, en la fricción cuántica entre átomos (modelizados como detectores de Unruh-deWitt) en un estado cuántico general en proximidad a una placa. Mostraré que, para velocidades relativas cercanas a c, la fricción cuántica diverge mientras que la fuerza de Casimir es casi independiente de la velocidad y como el tamaño finito del átomo nos elimina resultados infinitos espureos de la teoría. Además, obtenemos fricción cuántica incluso cuando el detector se encuentra aislado, pero sigue una trayectoria no inercial.
Resumen: En esta charla vamos a ver cómo usar Teoría de Campos y el formalismo de Scattering para estudiar diversos fenómenos físicos cuyo origen es la naturaleza cuántico-fluctuante del campo electromagnético (junto con la ruptura de simetrías translacionales y/o el no equilibrio termodinámico), como las fuerzas de Casimir y la emisibilidad y transferencia de calor entre cuerpos. En particular, tras una introducción teórica, me voy a centrar en el efecto Casimir y la trasferencia de calor entre materiales 2D de la familia del grafeno (con lo que veremos la importancia de la dimensionalidad y las propiedades de las respuestas electromagnéticas de los materiales) y, con un tratamiento relativista, en la fricción cuántica entre átomos (modelizados como detectores de Unruh-deWitt) en un estado cuántico general en proximidad a una placa. Mostraré que, para velocidades relativas cercanas a c, la fricción cuántica diverge mientras que la fuerza de Casimir es casi independiente de la velocidad y como el tamaño finito del átomo nos elimina resultados infinitos espureos de la teoría. Además, obtenemos fricción cuántica incluso cuando el detector se encuentra aislado, pero sigue una trayectoria no inercial.
Fecha
y hora: 13 de enero de 2020,
13:30 h.
Solving the sigma_8 tension with coupled quintessence
Ponente: Nelson Nunes
Filiación: IA/FCUL
Resumen: I will show that dark energy as a scalar field coupled to dark matter with Universe background evolution taken to be identical to the LambdaCDM one can alleviate the tension between the relatively high level of clustering found in cosmic microwave background observations and the smaller value obtained from large-scale observations in the late Universe. I will illustrate this using Redshift Space Distortions data and show forecast for Euclid, SKA and eRosita.
Resumen: I will show that dark energy as a scalar field coupled to dark matter with Universe background evolution taken to be identical to the LambdaCDM one can alleviate the tension between the relatively high level of clustering found in cosmic microwave background observations and the smaller value obtained from large-scale observations in the late Universe. I will illustrate this using Redshift Space Distortions data and show forecast for Euclid, SKA and eRosita.
Fecha
y hora: 16 de diciembre de 2019,
15:00 h.
Spectroscopy: a powerful tool to investigate the Universe
Ponente: José María Fernández Sánchez
Filiación: IEM-CSIC
Resumen: Hasta la detección de las ondas gravitacionales en 2016, todo nuestro conocimiento de los objetos astronómicos más allá del sistema solar provenía de la “luz” que nos llega de ellos. Esta radiación electromagnética contiene, en sus diversas regiones espectrales, mucha información detallada que solo se puede extraer mediante un análisis espectroscópico riguroso. En esta charla repasaremos el desarrollo histórico de la Espectroscopía, describiendo la información que se puede extraer de las distintas regiones espectrales, junto con la tecnología necesaria para su observación, tanto en tierra como desde satélites. Tras ello, presentaremos varios ejemplos de su aplicación a la Astrofísica, como la composición química de las estrellas, la detección de moléculas en el medio interestelar, el alejamiento de las galaxias, o la reciente detección de atmósferas en exoplanetas.
Resumen: Hasta la detección de las ondas gravitacionales en 2016, todo nuestro conocimiento de los objetos astronómicos más allá del sistema solar provenía de la “luz” que nos llega de ellos. Esta radiación electromagnética contiene, en sus diversas regiones espectrales, mucha información detallada que solo se puede extraer mediante un análisis espectroscópico riguroso. En esta charla repasaremos el desarrollo histórico de la Espectroscopía, describiendo la información que se puede extraer de las distintas regiones espectrales, junto con la tecnología necesaria para su observación, tanto en tierra como desde satélites. Tras ello, presentaremos varios ejemplos de su aplicación a la Astrofísica, como la composición química de las estrellas, la detección de moléculas en el medio interestelar, el alejamiento de las galaxias, o la reciente detección de atmósferas en exoplanetas.
Fecha
y hora: 2 de diciembre de 2019,
15:00 h.
Lugar: CSIC, CFMAC, sala de
conferencias (Serrano,
121)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2.ª planta)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2.ª planta)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2.ª planta)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar:Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (2.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (2.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica, sala de seminarios (2ª planta)
El
Sol, un gran desconocido
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (2ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lugar: CSIC,
CFMAC,
sala de juntas (c/ Serrano,
113 bis, 2º Planta)
Fractional Calculus as a Modelling Framework
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Pasado, Presente y Futuro de la Astronomía de Ondas Gravitacionales
Ponente: Carlos Sopuerta
Filiación: IEC-CSIC
Resumen: Las ondas gravitacionales son una predicción de la Teoría General de la Relatividad que Einstein completó en 1915. Hubo que esperar un siglo hasta que LIGO (Observatorio de Ondas Gravitacionales de Interferometría Láser) consiguiera realizar la primera detección. Este evento marcó el comienzo de la Astronomía de Ondas Gravitacionales (Premio Nobel de Física 2017) y aceleró el desarrollo de dectectores de diferentes tipos y diferentes tecnologías para cubrir las partes más importantes del espectro de dichas ondas. En este charla describiré los avances realizados hasta ahora en el desarrollo de observatorios de ondas gravitacionales, así como los que se esperan en las próximas dos décadas.
Resumen: Las ondas gravitacionales son una predicción de la Teoría General de la Relatividad que Einstein completó en 1915. Hubo que esperar un siglo hasta que LIGO (Observatorio de Ondas Gravitacionales de Interferometría Láser) consiguiera realizar la primera detección. Este evento marcó el comienzo de la Astronomía de Ondas Gravitacionales (Premio Nobel de Física 2017) y aceleró el desarrollo de dectectores de diferentes tipos y diferentes tecnologías para cubrir las partes más importantes del espectro de dichas ondas. En este charla describiré los avances realizados hasta ahora en el desarrollo de observatorios de ondas gravitacionales, así como los que se esperan en las próximas dos décadas.
Fecha
y hora: 19 de noviembre de 2019,
15:30 h.
Gravitational waves: A new window to observe the Universe
Ponente: Sachiko Kuroyanagi
Filiación: Universidad de Nagoya
Resumen: Gravitational waves, small ripples in the space time, are a new and unique observational tool for exploring unknown aspects of the universe. In the first part of my talk, I will review recent discoveries and developments of gravitational wave observation. Then I will introduce my data analysis activity in KAGRA collaboration for exploring relic gravitational waves from the early Universe, such as cosmic string bursts and a stochastic background.
Resumen: Gravitational waves, small ripples in the space time, are a new and unique observational tool for exploring unknown aspects of the universe. In the first part of my talk, I will review recent discoveries and developments of gravitational wave observation. Then I will introduce my data analysis activity in KAGRA collaboration for exploring relic gravitational waves from the early Universe, such as cosmic string bursts and a stochastic background.
Fecha
y hora: 4 de noviembre de 2019,
15:00 h.
Baryons, dark matter and black holes: a common origin
Ponente: Juan García-Bellido
Filiación: IFT-UAM/CSIC
Resumen: Twenty-three years ago, we predicted that massive primordial black holes (PBH) would form via the gravitational collapse of radiation and matter associated with high peaks in the spectrum of curvature fluctuations, and that they could constitute all of the dark matter (DM) today. In 2015, we predicted the clustering and broad mass distribution of PBH, which peaks at several Msun, and whose high-mass tails could be responsible for the seeds of all galaxies. Since then, AdvLIGO-Virgo interferometers have detected gravitational waves from at least thirty merger events of very massive and spinless black hole binaries, and we propose that they are PBH. We have recently understood that a universal mechanism associated with rapid changes in the number of relativistic species in the early universe could have been responsible for the formation of PBH at specific scales and thus have a very concrete prediction for the mass spectrum of DM-PBH, with broad peaks at 10^{-5}, 1, 100, and 10^6 Msun. In particular, the QCD quark-hadron transition could be responsible for the efficient production of baryons over antibaryons at PBH collapse, thus explaining the presence of baryons today and the relative abundance of DM to Baryons. We predict that, within a few months, a 100 Msun and a less than 1 Msun PBH will be detected by AdvLIGO-Virgo, and that in a few years an array of GW detectors could be used to determine the mass and spin distribution of PBH dark matter with 10% accuracy. Thus, gravitational wave astronomy could be responsible for a new paradigm shift in the understanding of the nature of dark matter and galaxy formation.
Resumen: Twenty-three years ago, we predicted that massive primordial black holes (PBH) would form via the gravitational collapse of radiation and matter associated with high peaks in the spectrum of curvature fluctuations, and that they could constitute all of the dark matter (DM) today. In 2015, we predicted the clustering and broad mass distribution of PBH, which peaks at several Msun, and whose high-mass tails could be responsible for the seeds of all galaxies. Since then, AdvLIGO-Virgo interferometers have detected gravitational waves from at least thirty merger events of very massive and spinless black hole binaries, and we propose that they are PBH. We have recently understood that a universal mechanism associated with rapid changes in the number of relativistic species in the early universe could have been responsible for the formation of PBH at specific scales and thus have a very concrete prediction for the mass spectrum of DM-PBH, with broad peaks at 10^{-5}, 1, 100, and 10^6 Msun. In particular, the QCD quark-hadron transition could be responsible for the efficient production of baryons over antibaryons at PBH collapse, thus explaining the presence of baryons today and the relative abundance of DM to Baryons. We predict that, within a few months, a 100 Msun and a less than 1 Msun PBH will be detected by AdvLIGO-Virgo, and that in a few years an array of GW detectors could be used to determine the mass and spin distribution of PBH dark matter with 10% accuracy. Thus, gravitational wave astronomy could be responsible for a new paradigm shift in the understanding of the nature of dark matter and galaxy formation.
Fecha
y hora: 28 de octubre de 2019,
15:00 h.
Galaxy evolution and cosmology using gamma rays observed with Fermi-LAT
Ponente: Alberto Domínguez
Filiación: UCM
Resumen: The light emitted by all galaxies across the history of the Universe is encoded in the intensity of the extragalactic background light (EBL), the diffuse cosmic radiation field at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for very high energy gamma rays via pair production, leaving a characteristic attenuation imprint in the spectra of distant gamma-ray sources. In this seminar, I will report on new measurements of the EBL using gamma-ray data from both the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and ground-based Imaging Atmospheric Cherenkov Telescopes. These unprecedented measurements have allowed us to derive the cosmic star-formation history, the number density of faint galaxies during the re-ionization epoch, and also the expansion rate of the Universe and its matter content. These results demonstrate that gamma-ray astrophysics has mature to the point of providing competitive measurements of cosmic properties previously restricted to techniques used by classical astronomy.
Resumen: The light emitted by all galaxies across the history of the Universe is encoded in the intensity of the extragalactic background light (EBL), the diffuse cosmic radiation field at ultraviolet, optical, and infrared wavelengths. The EBL is a source of opacity for very high energy gamma rays via pair production, leaving a characteristic attenuation imprint in the spectra of distant gamma-ray sources. In this seminar, I will report on new measurements of the EBL using gamma-ray data from both the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and ground-based Imaging Atmospheric Cherenkov Telescopes. These unprecedented measurements have allowed us to derive the cosmic star-formation history, the number density of faint galaxies during the re-ionization epoch, and also the expansion rate of the Universe and its matter content. These results demonstrate that gamma-ray astrophysics has mature to the point of providing competitive measurements of cosmic properties previously restricted to techniques used by classical astronomy.
Fecha
y hora: 7 de octubre de 2019,
15:00 h.
Loop Quantum Gravity: A Structural Overview
Ponente: Madhavan Varadarajan
Filiación: Raman Research Institute
Resumen: LQG is an attempt to construct a non-perturbative quantization of General Relativity. Rather than treat the quantum gravitational field as a quantum excitation over a fixed classical spacetime geometry, it seeks to construct the quantum mechanics of the gravitational field as a whole without recourse to any classical background spacetime geometry. In this talk I will focus on canonical LQG. I will provide a broad overview of its key structural features and their implications, and close with a brief description of my current research.
Resumen: LQG is an attempt to construct a non-perturbative quantization of General Relativity. Rather than treat the quantum gravitational field as a quantum excitation over a fixed classical spacetime geometry, it seeks to construct the quantum mechanics of the gravitational field as a whole without recourse to any classical background spacetime geometry. In this talk I will focus on canonical LQG. I will provide a broad overview of its key structural features and their implications, and close with a brief description of my current research.
Fecha
y hora: 26 de junio de 2019,
15:00 h.
Kerr-de Sitter spacetime and conformal infinity
Ponente: Marc Mars
Filiación: Universidad de Salamanca
Resumen: In this talk I will present several results concerning the characterization of the Kerr-de Sitter spacetime in terms of the asymptotic data at null infinity. This is relatively recent joint work with Paetz and Senovilla, and partially Simon. The first part of the talk is intended to be introductory: after reviewing the Kerr-de Sitter metric and recalling standard results on the initial value problem in General Relativity, I will discuss the initial value problem at past null infinity for the EFE with positive cosmological constant, as well as the notion of asymptotic Killing initial data. In the second part I will present the characterization results at infinity of Kerr-de Sitter based on a local characterization of this metric obtained a few years ago with Senovilla. If time permits I will also present recent results with Peón-Nieto on the higher dimensional case.
Resumen: In this talk I will present several results concerning the characterization of the Kerr-de Sitter spacetime in terms of the asymptotic data at null infinity. This is relatively recent joint work with Paetz and Senovilla, and partially Simon. The first part of the talk is intended to be introductory: after reviewing the Kerr-de Sitter metric and recalling standard results on the initial value problem in General Relativity, I will discuss the initial value problem at past null infinity for the EFE with positive cosmological constant, as well as the notion of asymptotic Killing initial data. In the second part I will present the characterization results at infinity of Kerr-de Sitter based on a local characterization of this metric obtained a few years ago with Senovilla. If time permits I will also present recent results with Peón-Nieto on the higher dimensional case.
Fecha
y hora: 13 de junio de 2019,
15:00 h.
Agujeros negros de Kruskal y su extensión cuántica
Ponente: Javier Olmedo
Filiación: Louisiana State University
Resumen: En esta charla resumiré las características principales de una nueva descripción cuántica efectiva para los espacio-tiempos de Kruskal. Centraré la discusión en agujeros negros con masas macroscópicas. En esta nueva descripción, las singularidades en las regiones "interiores" quedan resueltas de forma natural. Además, estos espacio-tiempos tienen las siguientes propiedades: (i) admiten un número infinito de regiones atrapadas, antiatrapadas y asintóticas; (ii) los escalares de curvatura más simples tienen cotas superiores independientes de la masa del agujero negro; (iii) en la región asintótica, la curvatura del espacio-tiempo cae lo suficientemente rápido para que la masa ADM esté bien definida; (iv) todas las regiones asintóticas tienen (cuantitativamente) la misma masa ADM (para agujeros negros macroscópicos). Finalmente, compararé esta propuesta con descripciones efectivas anteriores sugeridas en la literatura.
Resumen: En esta charla resumiré las características principales de una nueva descripción cuántica efectiva para los espacio-tiempos de Kruskal. Centraré la discusión en agujeros negros con masas macroscópicas. En esta nueva descripción, las singularidades en las regiones "interiores" quedan resueltas de forma natural. Además, estos espacio-tiempos tienen las siguientes propiedades: (i) admiten un número infinito de regiones atrapadas, antiatrapadas y asintóticas; (ii) los escalares de curvatura más simples tienen cotas superiores independientes de la masa del agujero negro; (iii) en la región asintótica, la curvatura del espacio-tiempo cae lo suficientemente rápido para que la masa ADM esté bien definida; (iv) todas las regiones asintóticas tienen (cuantitativamente) la misma masa ADM (para agujeros negros macroscópicos). Finalmente, compararé esta propuesta con descripciones efectivas anteriores sugeridas en la literatura.
Fecha
y hora: 28 de mayo de 2019,
15:00 h.
Asymptotically Safe Gravity: from astrophysics to cosmology
Ponente: Alessia Platania
Filiación: U. Heidelberg - ITP
Resumen: According to the "Asymptotic Safety conjecture", first postulated by Weinberg, quantization of gravity might result in a (non-perturbatively) renormalizable quantum field theory, whose high-energy limit is determined by a non-trivial fixed point of the gravitational renormalization group flow. The resulting scale-invariant regime implies an effective weakening of the gravitational interaction at high energies. This anti-screening behavior might have important implications in both astrophysics and cosmology. After reviewing the key ideas of the theory, in this talk I will discuss the phenomenological consequences of Asymptotically Safe Gravity, mostly focusing on the modifications induced by the running of the gravitational couplings in a black-hole interior and in the early evolution of the universe.
Resumen: According to the "Asymptotic Safety conjecture", first postulated by Weinberg, quantization of gravity might result in a (non-perturbatively) renormalizable quantum field theory, whose high-energy limit is determined by a non-trivial fixed point of the gravitational renormalization group flow. The resulting scale-invariant regime implies an effective weakening of the gravitational interaction at high energies. This anti-screening behavior might have important implications in both astrophysics and cosmology. After reviewing the key ideas of the theory, in this talk I will discuss the phenomenological consequences of Asymptotically Safe Gravity, mostly focusing on the modifications induced by the running of the gravitational couplings in a black-hole interior and in the early evolution of the universe.
Fecha
y hora: 9 de mayo de 2019,
15:00 h.
The challenge of indirect dark matter searches
Ponente: Ángeles Moliné
Filiación: IFT UAM-CSIC
Resumen: A tremendous amount of gravitational evidence for the existence of dark matter has been accumulated from astrophysical and cosmological observations. In the past decades, a huge effort has been focused on understanding its nature. Dark matter is searched for using a variety of complementary probes. In this talk, I will give a brief overview of the search methods, focusing on indirect dark matter searches which rely on astrophysical observations.
Resumen: A tremendous amount of gravitational evidence for the existence of dark matter has been accumulated from astrophysical and cosmological observations. In the past decades, a huge effort has been focused on understanding its nature. Dark matter is searched for using a variety of complementary probes. In this talk, I will give a brief overview of the search methods, focusing on indirect dark matter searches which rely on astrophysical observations.
Fecha
y hora: 25 de abril de 2019,
15:00 h.
Cosmology with the Dark Energy Survey
Ponente: Eusebio Sánchez Álvaro
Filiación: CIEMAT
Resumen: The discovery of the cosmic acceleration established LCDM as the standard cosmological paradigm. The most shocking consequence of this theory is the existence of new physics, beyond the Standard Model of particle physics, three times (cosmic inflation, dark matter and dark energy). This fact means that everything that has ever been directly observed makes up just 5% of the Universe content. The remaining 95% is formed by two different components: dark matter (25%) and dark energy (70%). The existence of the dark components is inferred from the effect they have on ordinary matter, but they have never been observed in the laboratory. Ongoing and planned cosmic surveys are designed to test LCDM and more generally to shed light on the physical nature of the dark sector. The Dark Energy Survey (DES) has mapped 300 million galaxies and tens of thousands of galaxy clusters in five filters (grizY ) over 5000 square-degrres (1/8 of the sky), and has discovered several thousand type Ia supernovae in a 27 square-degrees time-domain survey. DES uses several cosmological probes to test LCDM. Galaxy clustering (LSS) and weak gravitational lensing (WL) are two of the most powerful. Jointly, these complementary probes sample the underlying matter density field through the galaxy population and the distortion of light due to gravitational lensing. In this talk, the cosmological results from the combination of LSS and WL from the first year data (Y1) and the first results from the supernovae survey are presented. They have set strong constraints on LCDM and its simplest extensions. A very brief review of the final DES expectations and the cosmological projects for the near future are also presented.
Resumen: The discovery of the cosmic acceleration established LCDM as the standard cosmological paradigm. The most shocking consequence of this theory is the existence of new physics, beyond the Standard Model of particle physics, three times (cosmic inflation, dark matter and dark energy). This fact means that everything that has ever been directly observed makes up just 5% of the Universe content. The remaining 95% is formed by two different components: dark matter (25%) and dark energy (70%). The existence of the dark components is inferred from the effect they have on ordinary matter, but they have never been observed in the laboratory. Ongoing and planned cosmic surveys are designed to test LCDM and more generally to shed light on the physical nature of the dark sector. The Dark Energy Survey (DES) has mapped 300 million galaxies and tens of thousands of galaxy clusters in five filters (grizY ) over 5000 square-degrres (1/8 of the sky), and has discovered several thousand type Ia supernovae in a 27 square-degrees time-domain survey. DES uses several cosmological probes to test LCDM. Galaxy clustering (LSS) and weak gravitational lensing (WL) are two of the most powerful. Jointly, these complementary probes sample the underlying matter density field through the galaxy population and the distortion of light due to gravitational lensing. In this talk, the cosmological results from the combination of LSS and WL from the first year data (Y1) and the first results from the supernovae survey are presented. They have set strong constraints on LCDM and its simplest extensions. A very brief review of the final DES expectations and the cosmological projects for the near future are also presented.
Fecha
y hora: 11 de abril de 2019,
15:00 h.
Quantum simulation of traversable wormholes and exotic spacetimes
Ponente: Carlos Sabín
Filiación: IFF
Resumen: We present several schemes for analog quantum simulation of spacetimes containing traversable wormholes. First, we will consider a simluation by means of a dc-SQUID array. The impedance of the array places severe limitations on the type of spacetime that we can implement. The quantum fluctuations of the phase due to the impedance might be seen as an analogue of Hawking’s chronology protection mechanism. We will discuss as well possible applications of these techniques to different spacetime metrics of interest such as Gödel, Alcubierre and Kerr. Alternatively, we propose a recipe for the simulation in a Bose-Einstein condensate, both in 1+1 D and 3+1 D. Finally, we will also discuss a scheme for the quantum simulation of the single-particle Dirac equation in traversable wormholes and other exotic spacetimes.
Resumen: We present several schemes for analog quantum simulation of spacetimes containing traversable wormholes. First, we will consider a simluation by means of a dc-SQUID array. The impedance of the array places severe limitations on the type of spacetime that we can implement. The quantum fluctuations of the phase due to the impedance might be seen as an analogue of Hawking’s chronology protection mechanism. We will discuss as well possible applications of these techniques to different spacetime metrics of interest such as Gödel, Alcubierre and Kerr. Alternatively, we propose a recipe for the simulation in a Bose-Einstein condensate, both in 1+1 D and 3+1 D. Finally, we will also discuss a scheme for the quantum simulation of the single-particle Dirac equation in traversable wormholes and other exotic spacetimes.
Fecha
y hora: 28 de marzo de 2019,
15:00 h.
Entropía, información y ergodicidad
Ponente: Juan M. Rodríguez Parrondo
Filiación: UCM
Resumen: La relación entre información y entropía es un problema que ha afectado a los fundamentos de la termodinámica y la física estadística desde sus inicios. En 1867, Maxwell se dio cuenta de que un ser capaz de observar la posición y velocidad de las moléculas podía transferir energía de un gas frío a uno caliente sin trabajo, en aparente contradicción con la segunda ley de la termodinámica. Desde entonces se ha tratado de encontrar la manera de conciliar el "demonio de Maxwell" y la solución ha consistido en analizar el coste entrópico de procesos en los que la información juega un papel relevante, como la medición de un observable o el borrado de una memoria. En la charla repasaremos la historia del demonio de Maxwell, introduciremos el marco teórico más reciente en el que se puede formular una "termodinámica de la información" y discutiremos la relación entre la información y la pérdida de ergodicidad en un sistema físico.
Resumen: La relación entre información y entropía es un problema que ha afectado a los fundamentos de la termodinámica y la física estadística desde sus inicios. En 1867, Maxwell se dio cuenta de que un ser capaz de observar la posición y velocidad de las moléculas podía transferir energía de un gas frío a uno caliente sin trabajo, en aparente contradicción con la segunda ley de la termodinámica. Desde entonces se ha tratado de encontrar la manera de conciliar el "demonio de Maxwell" y la solución ha consistido en analizar el coste entrópico de procesos en los que la información juega un papel relevante, como la medición de un observable o el borrado de una memoria. En la charla repasaremos la historia del demonio de Maxwell, introduciremos el marco teórico más reciente en el que se puede formular una "termodinámica de la información" y discutiremos la relación entre la información y la pérdida de ergodicidad en un sistema físico.
Fecha
y hora: 14 de marzo de 2019,
15:00 h.
El
Sol, un gran desconocido
Ponente: Benjamín
Montesinos
Filiación: Centro
de Astrobiología, CSIC-INTA
Resumen: A pesar de ser la estrella más cercana, el Sol aún presenta muchos enigmas a los que dar respuesta. En este coloquio repasaremos algunos de ellos, haciendo un recorrido que describirá su formación -ligada a la del Sistema Solar en su conjunto- y evolución hasta la fase de enana blanca, su estructura y los fenómenos que dan origen a los complejos campos magnéticos, cuyas manifestaciones más conocidas son la manchas solares y los ciclos de aproximadamente 11 años. Nos detendremos en las interesantes anomalías en esa periodicidad -los llamados "grandes mínimos" [de actividad magnética]- sobre los que se han formulado hipótesis realmente provocativas. Pondremos al Sol en perspectiva comparándolo con otras estrelllas, y por supuesto, intentaremos contestar las dudas y curiosidades de la audiencia.
Resumen: A pesar de ser la estrella más cercana, el Sol aún presenta muchos enigmas a los que dar respuesta. En este coloquio repasaremos algunos de ellos, haciendo un recorrido que describirá su formación -ligada a la del Sistema Solar en su conjunto- y evolución hasta la fase de enana blanca, su estructura y los fenómenos que dan origen a los complejos campos magnéticos, cuyas manifestaciones más conocidas son la manchas solares y los ciclos de aproximadamente 11 años. Nos detendremos en las interesantes anomalías en esa periodicidad -los llamados "grandes mínimos" [de actividad magnética]- sobre los que se han formulado hipótesis realmente provocativas. Pondremos al Sol en perspectiva comparándolo con otras estrelllas, y por supuesto, intentaremos contestar las dudas y curiosidades de la audiencia.
Fecha
y hora: 28 de febrero de 2019,
15:00 h.
The Higgs, the Inflaton and their meeting at LHC
Ponente: Mindaugas Karciauskas
Filiación: UCM
Resumen: The current data favour metastability of the electroweak (EW) vacuum, which poses a number of cosmological challenges. We suggest a novel solution which does not employ any extra fields beyond the inflaton. We show that the Higgs mixing with an inflaton can lead to a stable EW vacuum. A trilinear Higgs–inflaton coupling always results in such a mixing and it is generally present in realistic models describing the reheating stage correctly. We find that cosmological constraints on this coupling are weak and an order one mixing is possible. In this case, the model is effectively described by a single mass scale of the EW size, making it particularly interesting for direct LHC searches.
Resumen: The current data favour metastability of the electroweak (EW) vacuum, which poses a number of cosmological challenges. We suggest a novel solution which does not employ any extra fields beyond the inflaton. We show that the Higgs mixing with an inflaton can lead to a stable EW vacuum. A trilinear Higgs–inflaton coupling always results in such a mixing and it is generally present in realistic models describing the reheating stage correctly. We find that cosmological constraints on this coupling are weak and an order one mixing is possible. In this case, the model is effectively described by a single mass scale of the EW size, making it particularly interesting for direct LHC searches.
Fecha
y hora: 14 de febrero de 2019,
15:00 h.
Consistent effective field theories and the Swampland
Ponente: Lavinia Heisenberg
Filiación: ETH Zurich
Resumen: After giving a systematical overview about consistent-looking constructions of effective field theories of gravity, I will discuss different ways of assessing them by means of theoretical and cosmological consistency. In the former caseI will pay special attention to the recently suggested Swampland criteria and their cosmological implications.
Resumen: After giving a systematical overview about consistent-looking constructions of effective field theories of gravity, I will discuss different ways of assessing them by means of theoretical and cosmological consistency. In the former caseI will pay special attention to the recently suggested Swampland criteria and their cosmological implications.
Fecha
y hora: 31 de enero de 2019,
15:00 h.
How does a black hole die? Cosmological and astrophysical consequences
Ponente: Francesca Vidotto
Filiación: Dept. de Física Teórica y de Historia de la Física, UPV/EHU
Resumen: Black holes are not forever: Hawking radiation or other instabilities of quantum-gravitational origin can make their life finite. I present a concrete realisation of how this can happen: the black-hole geometry can tunnel to a white-hole geometry. While the process is expected to be generic of all black holes, it becomes observationally relevant for primordial black holes. A first consequence of the proposed scenario is to shed light on how a remnant can form and be stable, providing a viable dark-matter candidate. Second, the white-hole phase can be accompanied by an explosion, that presents characteristic features allowing to distinguish it from other astrophysical sources. I discuss in particular a possible emission channel compatible with fast radio bursts. Interestingly, exploding primordial black holes constitute a peculiar kind of decaying dark matter, whose effects could appear in late-universe observations.
Resumen: Black holes are not forever: Hawking radiation or other instabilities of quantum-gravitational origin can make their life finite. I present a concrete realisation of how this can happen: the black-hole geometry can tunnel to a white-hole geometry. While the process is expected to be generic of all black holes, it becomes observationally relevant for primordial black holes. A first consequence of the proposed scenario is to shed light on how a remnant can form and be stable, providing a viable dark-matter candidate. Second, the white-hole phase can be accompanied by an explosion, that presents characteristic features allowing to distinguish it from other astrophysical sources. I discuss in particular a possible emission channel compatible with fast radio bursts. Interestingly, exploding primordial black holes constitute a peculiar kind of decaying dark matter, whose effects could appear in late-universe observations.
Fecha
y hora: 17 de enero de 2019,
15:00 h.
Can Relativity and Quantum Theory learn to speak the same language? The Hitchhiker’s Guide to Relativistic Quantum Information
Ponente: Eduardo Martín-Martínez
Filiación: University of Waterloo - Institute for Quantum Computing
Resumen: A 42 minutes talk about the field of Relativistic Quantum Information. What it aims to do, what challenges it faces and, most importantly, why should we care about it! Towels are optional, but recommended.
Resumen: A 42 minutes talk about the field of Relativistic Quantum Information. What it aims to do, what challenges it faces and, most importantly, why should we care about it! Towels are optional, but recommended.
Fecha
y hora: 20 de diciembre de 2018,
15:00 h.
Trazando el agujero negro en el Centro de la Vía Láctea a través de las estrellas masivas
Ponente: Francisco Najarro
Filiación: Centro de Astrobiología, CSIC-INTA
Resumen: En esta charla repasaremos como las observaciones de estrellas masivas, tanto en modo imagen como espectroscópico, han contribuido a caracterizar el agujero negro masivo en el centro de nuestra Galaxia a lo largo de las tres últimas decadas. Abarcaremos los primeros pasos en los que se dudaba de su existencia, continuando con la estimación más precisa de su masa y terminando por la deteccion de efectos post-newtoninanos recientes.
Resumen: En esta charla repasaremos como las observaciones de estrellas masivas, tanto en modo imagen como espectroscópico, han contribuido a caracterizar el agujero negro masivo en el centro de nuestra Galaxia a lo largo de las tres últimas decadas. Abarcaremos los primeros pasos en los que se dudaba de su existencia, continuando con la estimación más precisa de su masa y terminando por la deteccion de efectos post-newtoninanos recientes.
Fecha
y hora: 14 de diciembre de 2018,
15:00 h.
What gravitational collapse can tell us about quantum field theory thermalisation
Ponente: Esperanza López
Filiación: IFT UAM-CSIC
Resumen: The holographic principle has proven to be an extremely useful tool to study quantum field theory problems which are very hard to address which more conventional techniques. The far from equilibrium evolution of quantum systems is one of these areas. Remarkably, the holographic principle maps the dynamics of gravitational collapse with that of quantum field theory thermalization. It will be shown that holography is also able to model interesting processes with deviate from a fast approach to thermal equilibrium, known as quantum revivals.
Resumen: The holographic principle has proven to be an extremely useful tool to study quantum field theory problems which are very hard to address which more conventional techniques. The far from equilibrium evolution of quantum systems is one of these areas. Remarkably, the holographic principle maps the dynamics of gravitational collapse with that of quantum field theory thermalization. It will be shown that holography is also able to model interesting processes with deviate from a fast approach to thermal equilibrium, known as quantum revivals.
Fecha
y hora: 29 de noviembre de 2018,
15:00 h.
On the non-local surface plasmon contribution to the Casimir force
Ponente: Vincenzo Giannini
Filiación: IEM-CSIC
Resumen: The Casimir effect is a fundamental quantum-mechanical relativistic phenomenon which originates from the vacuum fluctuations of the electromagnetic field. It interconnects electrically neutral objects with or without permanent electric and/or magnetic moments. Using a quantum electrodynamical approach based on linear response theory we will show a detailed study of the Casimir force in graphene systems. Graphene is a two-dimensional crystal that has singular electronic, mechanical and optical properties. Being graphene a one atom thick structure makes particularly interesting to study Casimir forces between graphene sheets. The graphene sheets are considered as infinitesimal thin, local and isotropic conductive surfaces and furthermore, the influence of surface plasmons is explored. We will see how this fundamental effect depends on the graphene optical response and the gap. In this way, we are able to study the light-plasmon mediated interaction between graphene sheets. These results are particularly relevant for graphene nanotechnology applications.
Resumen: The Casimir effect is a fundamental quantum-mechanical relativistic phenomenon which originates from the vacuum fluctuations of the electromagnetic field. It interconnects electrically neutral objects with or without permanent electric and/or magnetic moments. Using a quantum electrodynamical approach based on linear response theory we will show a detailed study of the Casimir force in graphene systems. Graphene is a two-dimensional crystal that has singular electronic, mechanical and optical properties. Being graphene a one atom thick structure makes particularly interesting to study Casimir forces between graphene sheets. The graphene sheets are considered as infinitesimal thin, local and isotropic conductive surfaces and furthermore, the influence of surface plasmons is explored. We will see how this fundamental effect depends on the graphene optical response and the gap. In this way, we are able to study the light-plasmon mediated interaction between graphene sheets. These results are particularly relevant for graphene nanotechnology applications.
Fecha
y hora: 15 de noviembre de 2018,
15:00 h.
Un breve recorrido por la cuantización de campos en fondos curvos
Ponente: Jerónimo Cortez
Filiación: Universidad Nacional
Autónoma de México (UNAM)
Resumen: En esta charla revisaremos algunos aspectos sobre la cuantización de campos en fondos curvos. En particular, en lo que al proceso de cuantización en espacio de Hilbert se refiere, veremos el problema de unicidad y cómo puede sortearse a través de la imposición de criterios físicos. Aprovecharemos el recorrido para mencionar también algunas aplicaciones en gravedad, concretamente en la cuantización de modelos de simetría reducida cosmológicos.
Resumen: En esta charla revisaremos algunos aspectos sobre la cuantización de campos en fondos curvos. En particular, en lo que al proceso de cuantización en espacio de Hilbert se refiere, veremos el problema de unicidad y cómo puede sortearse a través de la imposición de criterios físicos. Aprovecharemos el recorrido para mencionar también algunas aplicaciones en gravedad, concretamente en la cuantización de modelos de simetría reducida cosmológicos.
Fecha
y hora: 18 de octubre de 2018,
15:00 h.
No LIGO MACHO: the Dark Universe in the Gravitational Wave Era
Ponente: Miguel Zumalacárregui
Filiación: UC Berkeley & IPhT
Saclay
Resumen: Evidence shows that we live in a universe where 95% of the matter and energy is of unknown nature. Right from the onset, Gravitational Wave (GW) astronomy is shaping our understanding of the dark universe in several ways: GW signals of black hole mergers have resurrected the idea of Dark Matter being made of primordial black holes, while multi-messenger GW astronomy has generated novel ways to test Dark Energy and the fundamental properties of gravity. I will discuss the impact of gravitational waves on the landscape of gravitational theories, and how the recent observation of a neutron star merger spectacularly rules out a large class of Dark Energy models in which the speed of GWs is variable, including some (otherwise viable) contenders to the cosmological constant. Then I will present how gravitational lensing of distant supernovae constrains the abundance of primordial black holes, which can not be the dominant form of Dark Matter.
Resumen: Evidence shows that we live in a universe where 95% of the matter and energy is of unknown nature. Right from the onset, Gravitational Wave (GW) astronomy is shaping our understanding of the dark universe in several ways: GW signals of black hole mergers have resurrected the idea of Dark Matter being made of primordial black holes, while multi-messenger GW astronomy has generated novel ways to test Dark Energy and the fundamental properties of gravity. I will discuss the impact of gravitational waves on the landscape of gravitational theories, and how the recent observation of a neutron star merger spectacularly rules out a large class of Dark Energy models in which the speed of GWs is variable, including some (otherwise viable) contenders to the cosmological constant. Then I will present how gravitational lensing of distant supernovae constrains the abundance of primordial black holes, which can not be the dominant form of Dark Matter.
Fecha
y hora: 12 de julio de 2018,
15:00 h.
Avances recientes en gravedad cuántica de lazos con simetría esférica
Ponente: Jorge Pullin
Filiación: Louisiana State University
Resumen: Detallaremos recientes resultados en gravedad cuántica de lazos con simetría esférica, incluyendo la solución exacta de las ecuaciones cuánticas de Einstein, el tratamiento de campos cuánticos que viven en la misma, el efecto Casimir, la radiación de Hawking y la evolución de cáscaras nulas como modelo de colapso, así como las implicaciones para la paradoja de la información.
Resumen: Detallaremos recientes resultados en gravedad cuántica de lazos con simetría esférica, incluyendo la solución exacta de las ecuaciones cuánticas de Einstein, el tratamiento de campos cuánticos que viven en la misma, el efecto Casimir, la radiación de Hawking y la evolución de cáscaras nulas como modelo de colapso, así como las implicaciones para la paradoja de la información.
Fecha
y hora: 11 de julio de 2018,
15:00 h.
Thermal scalar fields under gravitational effects
Ponente: Franco Dante Albareti
Filiación: IFT UAM-CSIC
Resumen: Within the framework of QFT in curved spacetimes, we compute one-loop corrections to the effective potential and energy-momentum tensor of a generically selfinteracting scalar field in a perturbed Robertson-Walker background. Vacuum and finite temperature contributions are described. An explicit mode decomposition of the field in the perturbed geometry is used instead of the local approach based on the Schwinger-De Witt expansion. The potential generation of
inhomogeneities in the vacuum
expectation value is also discussed.
Resumen: Within the framework of QFT in curved spacetimes, we compute one-loop corrections to the effective potential and energy-momentum tensor of a generically selfinteracting scalar field in a perturbed Robertson-Walker background. Vacuum and finite temperature contributions are described. An explicit mode decomposition of the field in the perturbed geometry is used instead of the local approach based on the Schwinger-De Witt expansion. The potential generation of
No LIGO MACHO: the Dark Universe in the Gravitational Wave Era
Speaker: Miguel Zumalacárregui
Affiliation: Louisiana State University
Abstract: Evidence shows that we live in a universe where 95% of the matter and energy is of unknown nature. Right from the onset, Gravitational Wave (GW) astronomy is shaping our understanding of the dark universe in several ways: GW signals of black hole mergers have resurrected the idea of Dark Matter being made of primordial black holes, while multi-messenger GW astronomy has generated novel ways to test Dark Energy and the fundamental properties of gravity. I will discuss the impact of gravitational waves on the landscape of gravitational theories, and how the recent observation of a neutron star merger spectacularly rules out a large class of Dark Energy models in which the speed of GWs is variable, including some (otherwise viable) contenders to the cosmological constant. Then I will present how gravitational lensing of distant supernovae constrains the abundance of primordial black holes, which can not be the dominant form of Dark Matter.
Abstract: Evidence shows that we live in a universe where 95% of the matter and energy is of unknown nature. Right from the onset, Gravitational Wave (GW) astronomy is shaping our understanding of the dark universe in several ways: GW signals of black hole mergers have resurrected the idea of Dark Matter being made of primordial black holes, while multi-messenger GW astronomy has generated novel ways to test Dark Energy and the fundamental properties of gravity. I will discuss the impact of gravitational waves on the landscape of gravitational theories, and how the recent observation of a neutron star merger spectacularly rules out a large class of Dark Energy models in which the speed of GWs is variable, including some (otherwise viable) contenders to the cosmological constant. Then I will present how gravitational lensing of distant supernovae constrains the abundance of primordial black holes, which can not be the dominant form of Dark Matter.
Date
and time: 12 July 2018,
15:00 h.
Venue: UCM, Faculty of Physical Sciences,
Theoretical Physics I Dept., seminar room (3rd floor)
Fecha
y hora: 28 de junio de 2018,
15:00 h.
Black hole evaporation: Entropy analysis and GUP corrections
Ponente: Ana Alonso Serrano
Filiación: AEI - Potsdam
Resumen: We have studied the entropy budget per particle emitted in blackbody radiation and determined explicit coarse-grainning models for classical and quantum entropies. As the process is unitary, the entropy is exactly compensated by the “hidden information” in the correlations that we choose not to consider within the specific selected coarse-graining. Our goal is to extend these ideas to a black hole evaporation process. In order to carry out this calculation we adopted a variant of the “average subsystem” approach, but consider a multipartite pure system that includes the influence of the rest of the universe. In addition, the entropy budget should be corrected at the last stages of evaporation, due to quantum gravity effects. We have been shown recently how these effects (expressed in terms of the generalized uncertainty principle) modify the Hawking flux when we approach the Planck size.
Resumen: We have studied the entropy budget per particle emitted in blackbody radiation and determined explicit coarse-grainning models for classical and quantum entropies. As the process is unitary, the entropy is exactly compensated by the “hidden information” in the correlations that we choose not to consider within the specific selected coarse-graining. Our goal is to extend these ideas to a black hole evaporation process. In order to carry out this calculation we adopted a variant of the “average subsystem” approach, but consider a multipartite pure system that includes the influence of the rest of the universe. In addition, the entropy budget should be corrected at the last stages of evaporation, due to quantum gravity effects. We have been shown recently how these effects (expressed in terms of the generalized uncertainty principle) modify the Hawking flux when we approach the Planck size.
Fecha
y hora: 14 de junio de 2018,
15:00 h.
Dark energy from α-attractors: phenomenology and observational constraints
Ponente: Carlos García
Filiación: IFF - CSIC
Resumen: The possibility of linking inflation and late cosmic accelerated expansion using the alpha-attractor models has received increasing attention due to their physical motivation. In the early universe, \alpha-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally alpha-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this talk we study a generalized dark energy alpha-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that 1+w\sim 1/\alpha (while the gravitational wave power r\sim\alpha) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 compressed likelihood), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions.
Resumen: The possibility of linking inflation and late cosmic accelerated expansion using the alpha-attractor models has received increasing attention due to their physical motivation. In the early universe, \alpha-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally alpha-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this talk we study a generalized dark energy alpha-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that 1+w\sim 1/\alpha (while the gravitational wave power r\sim\alpha) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 compressed likelihood), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions.
Fecha
y hora: 31 de mayo de 2018,
15:00 h.
Inflation and initial conditions: the role of fluctuation-dissipation dynamics
Ponente: Mar Bastero Gil
Filiación: Universidad de Granada
Resumen: In this talk we review the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider, in particular, that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. This may lead to a later perior of thermal inflation, which suppresses the effects of nonlinear interactions. between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime.
Resumen: In this talk we review the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider, in particular, that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. This may lead to a later perior of thermal inflation, which suppresses the effects of nonlinear interactions. between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime.
Fecha
y hora: 17 de mayo de 2018,
15:00 h.
Loop gravity without spin networks
Ponente: Wolfgang Wieland
Filiación: Perimeter Institute
Resumen: It is arguably one of the main achievements of loop quantum gravity to have demonstrated that space itself may have an atomic structure. One of the key open problems of the theory is to reconcile the fundamental loop quantum gravity discreteness of space with general relativity in the continuum. In this talk, I present recent progress regarding this issue: I will show that the loop gravity discreteness of space can be understood from a conventional Fock quantisation of gravitational boundary modes on a null surface. These boundary modes are found by considering a quasi-local Hamiltonian analysis, where general relativity is treated as a Hamiltonian system in domains with inner null boundaries. The presence of such null boundaries requires then additional boundary terms in the action. Using Ashtekar’s original SL(2,C) self-dual variables, I will explain that the natural such boundary term is nothing but a kinetic term for a spinor (defining the null flag of the boundary) and a spinor-valued two-form, which are both intrinsic to the boundary. Finally, I will show that in quantum theory, the cross-sectional area two-form turns into the difference of two number operators (unless the Barbero—Immirzi parameter is sent to infinity). The resulting area spectrum is discrete without ever introducing spin networks or triangulations of space.
Resumen: It is arguably one of the main achievements of loop quantum gravity to have demonstrated that space itself may have an atomic structure. One of the key open problems of the theory is to reconcile the fundamental loop quantum gravity discreteness of space with general relativity in the continuum. In this talk, I present recent progress regarding this issue: I will show that the loop gravity discreteness of space can be understood from a conventional Fock quantisation of gravitational boundary modes on a null surface. These boundary modes are found by considering a quasi-local Hamiltonian analysis, where general relativity is treated as a Hamiltonian system in domains with inner null boundaries. The presence of such null boundaries requires then additional boundary terms in the action. Using Ashtekar’s original SL(2,C) self-dual variables, I will explain that the natural such boundary term is nothing but a kinetic term for a spinor (defining the null flag of the boundary) and a spinor-valued two-form, which are both intrinsic to the boundary. Finally, I will show that in quantum theory, the cross-sectional area two-form turns into the difference of two number operators (unless the Barbero—Immirzi parameter is sent to infinity). The resulting area spectrum is discrete without ever introducing spin networks or triangulations of space.
Fecha
y hora: 3 de mayo de 2018,
15:00 h.
Taming the beast: initial conditions and degrees of freedom in non-local gravity
Ponente: Gianluca Calcagni
Filiación: IEM, CSIC
Resumen: Non-local quantum gravity is a class of fundamental theories whose classical and quantum dynamics is specified by "form factors", operators with infinitely many derivatives. After briefly reviewing this paradigm and its role in the resolution of big-bang and black-hole singularities, for the first time we count the number of nonpertubative field degrees of freedom as well as the number of initial conditions to be specified to solve the Cauchy problem. In particular, in four dimensions and for the string-related form factor, there are 8 degrees of freedom (2 graviton polarization mode and 6 rank-2 tensor modes) and 4 initial conditions. The method to obtain this result is first illustrated in a pedagogical way for the case of a non-local scalar field. Consequences for cosmology and astrophysics are discussed.
Resumen: Non-local quantum gravity is a class of fundamental theories whose classical and quantum dynamics is specified by "form factors", operators with infinitely many derivatives. After briefly reviewing this paradigm and its role in the resolution of big-bang and black-hole singularities, for the first time we count the number of nonpertubative field degrees of freedom as well as the number of initial conditions to be specified to solve the Cauchy problem. In particular, in four dimensions and for the string-related form factor, there are 8 degrees of freedom (2 graviton polarization mode and 6 rank-2 tensor modes) and 4 initial conditions. The method to obtain this result is first illustrated in a pedagogical way for the case of a non-local scalar field. Consequences for cosmology and astrophysics are discussed.
Fecha
y hora: 19 de abril de 2018,
16:00 h.
Towards new constraints in extended theories of gravity: large-scale structures, neutron stars and SKA
Ponente: Álvaro de la Cruz-Dombriz
Filiación: U. of Cape Town and SKA Cosmology
Resumen: Model-independent methods in cosmology, N-body simulations and theoretical predictions in strong-gravity regimes have become essentials tool in order to deal with an increasing number of theoretical alternatives for explaining several open issues in the cosmic history. In principle, this provides a way of testing the ΛCDM cosmological paradigm under different assumptions and to rule out whole classes of competing theories. In this talk I will present some of the latest progress and shortcomings in a recent line of full N-body simulation technique modifying g-evolution to accommodate effects from higher-order theories. Then, I will provide a flavour on the phenomenology of neutron stars in scalar-tensor gravity theories and the potentiality of SKA to detect large-scale structure effects beyond the Einsteinian paradigm.
Resumen: Model-independent methods in cosmology, N-body simulations and theoretical predictions in strong-gravity regimes have become essentials tool in order to deal with an increasing number of theoretical alternatives for explaining several open issues in the cosmic history. In principle, this provides a way of testing the ΛCDM cosmological paradigm under different assumptions and to rule out whole classes of competing theories. In this talk I will present some of the latest progress and shortcomings in a recent line of full N-body simulation technique modifying g-evolution to accommodate effects from higher-order theories. Then, I will provide a flavour on the phenomenology of neutron stars in scalar-tensor gravity theories and the potentiality of SKA to detect large-scale structure effects beyond the Einsteinian paradigm.
Fecha
y hora: 5 de abril de 2018,
15:00 h.
Testing the Dark Universe with Gravitational Waves
Ponente: Jose María Ezquiaga
Filiación: IFT, CSIC-UAM
Resumen: Gravitational wave (GW) astronomy has come to revolutionize our understanding of astrophysics, cosmology and fundamental physics. GWs from binary black-hole (BH) mergers allow us to learn about the population of BHs, their origin and their role through the history of the universe. If these BHs have a primordial origin and are abundant enough, they could comprise a large fraction of the Dark Matter (DM). As a case of study, I will present the primordial black-hole production in Critical Higgs Inflation, a particle physics motivated model in which the SM Higgs is both responsible of inflation and DM, and discuss its GWs signatures. Moreover, GWs detected with an associated counterpart can probe the evolution of the universe and Dark Energy (DE). The recent measurement of the GW speed following GW170817 is an excellent example of the immense potential available to GWs tests of gravity. I will present the conditions for anomalous GW speed and classify the theories for DE that remain viable after GW170817. Finally, I will discuss how other propagation effects could also shed light on the quest for the nature of DE.
Resumen: Gravitational wave (GW) astronomy has come to revolutionize our understanding of astrophysics, cosmology and fundamental physics. GWs from binary black-hole (BH) mergers allow us to learn about the population of BHs, their origin and their role through the history of the universe. If these BHs have a primordial origin and are abundant enough, they could comprise a large fraction of the Dark Matter (DM). As a case of study, I will present the primordial black-hole production in Critical Higgs Inflation, a particle physics motivated model in which the SM Higgs is both responsible of inflation and DM, and discuss its GWs signatures. Moreover, GWs detected with an associated counterpart can probe the evolution of the universe and Dark Energy (DE). The recent measurement of the GW speed following GW170817 is an excellent example of the immense potential available to GWs tests of gravity. I will present the conditions for anomalous GW speed and classify the theories for DE that remain viable after GW170817. Finally, I will discuss how other propagation effects could also shed light on the quest for the nature of DE.
Fecha
y hora: 8 de marzo de 2018,
15:00 h.
Primordial fluctuations in Loop Quantum Cosmology
Ponente: Mercedes Martín-Benito
Filiación: UCM
Resumen: A lot of attention has been devoted lately to the consideration of quantum corrections to the power spectrum of primordial fluctuations, as a possible window to unveil quantum geometry phenomena in the Early Universe. In this talk I will review the derivation of these corrections in the framework of hybrid Loop Quantum Cosmology (LQC). Homogeneous LQC provides a canonical quantization for FLRW models free of singularities: the classical big bang singularity is replaced by a quantum bounce, the quantum dynamics is everywhere well-defined, and physical observables never diverge. On the other hand, hybrid LQC extends the LQC quantization to systems with inhomogeneities. For the particular case of cosmological perturbations in flat FLRW supplemented with inflation, I will analyze the quantum dynamics of states that verify a Born-Oppenheimer ansatz. They describe a regime where the cosmological perturbations can be regarded as a field propagating over a homogeneous quantum geometry. From those states, we will recover a Mukhanov-Sasaki equation for cosmological perturbations that incorporates the mentioned quantum corrections. Such corrections are encoded in the expectation value of operators of the homogeneous geometry. I will discuss how these corrections might lead to observational imprints in the primordial power spectra.
Resumen: A lot of attention has been devoted lately to the consideration of quantum corrections to the power spectrum of primordial fluctuations, as a possible window to unveil quantum geometry phenomena in the Early Universe. In this talk I will review the derivation of these corrections in the framework of hybrid Loop Quantum Cosmology (LQC). Homogeneous LQC provides a canonical quantization for FLRW models free of singularities: the classical big bang singularity is replaced by a quantum bounce, the quantum dynamics is everywhere well-defined, and physical observables never diverge. On the other hand, hybrid LQC extends the LQC quantization to systems with inhomogeneities. For the particular case of cosmological perturbations in flat FLRW supplemented with inflation, I will analyze the quantum dynamics of states that verify a Born-Oppenheimer ansatz. They describe a regime where the cosmological perturbations can be regarded as a field propagating over a homogeneous quantum geometry. From those states, we will recover a Mukhanov-Sasaki equation for cosmological perturbations that incorporates the mentioned quantum corrections. Such corrections are encoded in the expectation value of operators of the homogeneous geometry. I will discuss how these corrections might lead to observational imprints in the primordial power spectra.
Fecha
y hora: 22 de febrero de 2018,
15:00 h.
From LISA Pathfinder to LISA: Enabling the Science of the Gravitational-Wave Low-Frequency Band
Ponente: Carlos Sopuerta
Filiación: ICE-CSIC, Universidad Autónoma de Barcelona
Resumen: LIGO and Virgo have inaugurated the era of Gravitational Wave Astronomy by observing several binary black hole mergers and the merger of a neutron star binary that has made possible multimessenger astronomy with gravitational waves. Apart from the initial discovery, these detections have produced revolutionary discoveries. At the same time, there are ongoing efforts to detect gravitational waves beyond the high-frequency band of the ground-based detectors. Indeed, after the success of the LISA Pathfinder mission, the European Space Agency has selected LISA (Laser Interferometer Space Antenna) as its third large-classe mission (L3). The main goal of LISA is to carry out the science proposed in the white paper "The Gravitational Universe", consisting in low-frequency gravitational-wave astronomy. In this talk I will describe the main scientific goals of the mission and its potential for new discoveries in astrophysics,
cosmology, and fundamental physics.
Resumen: LIGO and Virgo have inaugurated the era of Gravitational Wave Astronomy by observing several binary black hole mergers and the merger of a neutron star binary that has made possible multimessenger astronomy with gravitational waves. Apart from the initial discovery, these detections have produced revolutionary discoveries. At the same time, there are ongoing efforts to detect gravitational waves beyond the high-frequency band of the ground-based detectors. Indeed, after the success of the LISA Pathfinder mission, the European Space Agency has selected LISA (Laser Interferometer Space Antenna) as its third large-classe mission (L3). The main goal of LISA is to carry out the science proposed in the white paper "The Gravitational Universe", consisting in low-frequency gravitational-wave astronomy. In this talk I will describe the main scientific goals of the mission and its potential for new discoveries in astrophysics,
cosmology, and fundamental physics.
Fecha
y hora:
Fractional Calculus as a Modelling Framework
Ponente: Luis Vázquez
Filiación: Universidad Complutense de Madrid
Resumen: The Fractional Calculus represents a natural instrument to model nonlocal phenomena either in space or time. From Physics and Chemistry to Biology and Engineering, there are many processes that involve different space / time scales. In many cases, the dynamics of such systems can be formulated by fractional differential equations which include the nonlocal effects. We give a panoramic view of the field with associated challenges and applications in the studies of metamaterials as well as in Martian studies.
Resumen: The Fractional Calculus represents a natural instrument to model nonlocal phenomena either in space or time. From Physics and Chemistry to Biology and Engineering, there are many processes that involve different space / time scales. In many cases, the dynamics of such systems can be formulated by fractional differential equations which include the nonlocal effects. We give a panoramic view of the field with associated challenges and applications in the studies of metamaterials as well as in Martian studies.
Fecha
y hora:
Astrofísica gamma y física fundamental con MAGIC
Ponente: Marcos López Moya
Filiación:
Universidad Complutense de Madrid
Resumen: La Astrofísica gamma nos abre una ventana a los fenómenos más violentos del universo, que suelen surgir en la vecindad de objetos cósmicos muy masivos y compactos, como agujeros negros, estrellas de neutrones o explosiones supernova, acelerando partículas hasta energías ultrarrelativistas. Entre los detectores actuales de rayos gamma destacan los telescopios MAGIC, situados en la isla de La Palma, con los que se han descubierto multitud de fuentes, tanto de origen galáctico como extragaláctico. Pero, además, estos telescopios permiten abordar cuestiones de física fundamental, como la búsqueda de materia oscura e incluso sondear la estructura microscópica del espacio-tiempo postulada por algunos modelos de gravedad cuántica. Según estos modelos, la velocidad de la luz debería depender ligeramente de la energía de los fotones. De ser el caso, tales cambios tendrían que plasmarse en los tiempos de llegada de los fotones de distintas energías detectados por los telescopios. En esta charla daremos una visión general del campo, destacando los logros conseguidos con MAGIC en cuestiones tales como los límites a la violación de la invariancia Lorentz.
Resumen: La Astrofísica gamma nos abre una ventana a los fenómenos más violentos del universo, que suelen surgir en la vecindad de objetos cósmicos muy masivos y compactos, como agujeros negros, estrellas de neutrones o explosiones supernova, acelerando partículas hasta energías ultrarrelativistas. Entre los detectores actuales de rayos gamma destacan los telescopios MAGIC, situados en la isla de La Palma, con los que se han descubierto multitud de fuentes, tanto de origen galáctico como extragaláctico. Pero, además, estos telescopios permiten abordar cuestiones de física fundamental, como la búsqueda de materia oscura e incluso sondear la estructura microscópica del espacio-tiempo postulada por algunos modelos de gravedad cuántica. Según estos modelos, la velocidad de la luz debería depender ligeramente de la energía de los fotones. De ser el caso, tales cambios tendrían que plasmarse en los tiempos de llegada de los fotones de distintas energías detectados por los telescopios. En esta charla daremos una visión general del campo, destacando los logros conseguidos con MAGIC en cuestiones tales como los límites a la violación de la invariancia Lorentz.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Coincident General Relativity
Ponente: Tomi Koivisto
Filiación: Nordita
Resumen: The Palatini formalism is applied to generate
teleparallel and symmetric teleparallel theories of gravity
without introducing frame elds. From the symmetric version an
exceptional class is discovered, which is consistent with a
completely vanishing ane connection. We use this remarkable
property in this Letter to propose a simpler geometrical
formulation of General Relativity that is oblivious to the
structure of the spacetime, thus fundamentally depriving gravity
from any inertial character. The resulting theory is described by
the Einstein-Hilbert action purged from the boundary term and is
more robustly underpinned by the spin-2 eld theory. We also show
that this construction gives a natural starting point for modied
gravity theories and present new and simple generalisations where
analytical self-accelerating cosmological solutions arise
naturally in the early and late time universe cosmology.
Fecha
y hora: 21 de diciembre de
2017, 15:30 h.
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Computational Complexity and Holography
Ponente: José L.F. Barbón
Filiación: IFT,
UAM-CSIC
Resumen: I will review recent ideas in holography, imported from the
theory of quantum complexity, mainly in the context of AdS/CFT
correspondences. In particular, I will discuss various competing
prescriptions to defineholographic versions of quantum complexity.
Fecha
y hora: 30 de noviembre de
2017, 15:00 h.
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Gravitational waves. What's in for hadron physics?
Ponente: Felipe J. Llanes Estrada
Filiación: Universidad Complutense de Madrid
Resumen: The finding of Gravitational Waves by the aLIGO scientific and VIRGO
collaborations opens opportunities to better test and understand strong
interactions, both nuclear-hadronic and gravitational. Assuming
General Relativity holds, one can constrain hadron physics at a neutron
star. But precise knowledge of the Equation of State and transport
properties in hadron matter can also reverse the logic and be used to constrain the theory of
gravity itself. I make an amateur review of a couple of these opportunities in the context
of modified f(R) gravity, the maximum mass of neutron stars, and
progress in the Equation of State of neutron matter from the effective theories of QCD.
Fecha
y hora: 16 de noviembre de
2017, 15:00 h.
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Forecast and analysis of the cosmological redshift drift
Ponente: Ruth Lazkoz
Filiación:
Universidad del País Vasco (UPV/EHU), Leioa
Resumen: The cosmological redshift drift could lead to the next step in high-precision cosmic
geometric observations, becoming a direct and irrefutable test for cosmic acceleration. In
order to test the viability and possible properties of this effect, also called Sandage-Loeb
(SL) test, we generate a model independent mock data set so as to compare its
constraining power with that of the future mock data sets of Type Ia Supernovae (SNe)
and Baryon Acoustic Oscillations (BAO). The performance of those data sets is analyzed
by testing several cosmological models with Markov chain Monte Carlo (MCMC), both
independently and combining all data sets. Final results show that, in general, SL data sets
present allow for remarkable constrains on the matter density parameter today on every
tested model, showing also a great complementarity with SNe and BAO data regarding
dark energy (DE) parameters.
Early Universe with a Born-Infeld taste
Ponente: Jose Beltrán
Filiación:
Instituto de Física Teórica (IFT-CSIC), Madrid
Resumen:
In order to
regularize the energy of point-like charged particles, Born and Infeld
introduced a modification of the Maxwell Lagrangian that naturally
imposes an upper bound on electromagnetic fields. Similar ideas can be
applied to gravity to resolve the GR singularities. I will discuss some
general theoretical aspects of these theories (which are shared by more
general metric-affine theories) as well as some cosmological
applications, with emphasis in non-singular and inflationary solutions.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Lorentz invariance and the zero-point stress-energy
Ponente: Matt Visser
Filiación: Victoria
University of Wellington, New Zealand
Resumen:
Some 65 years
ago (1951) Wolfgang Pauli noted that the zero-point energy density
could be set to zero by a carefully fine-tuned cancellation between
bosons and fermions. In this seminar I will argue in a slightly
different direction: The zero-point energy density is only one
component of the zero-point stress energy tensor, and it is this tensor
quantity that is in many ways the more fundamental object of interest.
I shall demonstrate that Lorentz invariance of the zero-point stress
energy tensor implies finiteness of the zero-point stress energy
tensro, and viceversa.
Fecha y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Properties of Rotating Black Holes in Odd Dimensions
Ponente: Paco Navarro
Filiación:
Universidad Complutense de Madrid
Resumen:
On this talk,
we will discuss about the properties of rotating Abelian black holes in
odd-dimensional spacetimes, and show how the case when all angular
momenta are equal becomes much simpler. This simplification also
applies to theories with Chern-Simons terms, a cosmological constant,
or scalar fields.
We will concentrate on the effects that do not appear in 4 dimensions and address subjects such as non-uniqueness, near-horizon geometry, radially excited solutions, etc.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
The smooth and clumpy universe: present and asymptotic behaviour(s)
Ponente: Mariam Bouhmadi
López
Filiación:
Universidad del País Vasco (UPV/EHU), IKERBASQUE
Resumen:
On this talk,
we will present a review on dark energy singularities and abrupt
events. We will start with a classical description of several models,
including their behaviour at the perturbative level. Then, we will
contrast our results with observational data. On the second part of the
talk, we will focus on the quantum analysis of these
singularities/abrupt events. The analysis will encompass also modified
theories of gravity. Finally, if time allows, we will as well show how
phantom dark energy models might not at all imply dark energy
singularities in Einstein-Cartan theory.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Deformed relativistic symmetries: decoherence and dimensional reduction at the Planck scale
Ponente: Michele Arzano
Filiación:
Universidad de Roma - La Sapienza, Italia
Resumen:
I will start
with a brief introduction to the framework of deformed relativistic
symmetries based on Lie-group momentum spaces whose curvature sets a
fundamental (Planckian) UV scale at the kinematical level. I will then
show how these models can be related to a fundamental decoherence at
the Planck scale and how they are relevant for the phenomenon of
“dimensional reduction”, ubiquitous in a variety of approaches to
quantum gravity.
Tension and constraints on modified gravity parametrizations of Geff(z) from growth rate and Planck data
Ponente: Savvas Nesseris
Filiación:
Instituto de Física Teórica (IFT-CSIC), Madrid
Resumen:
Some of the
current cosmological data, i.e. weak lensing (WL), growth rate, seem to
be in tension with Planck15/LCDM and indicate consistently that there
is a lack of gravitational power in structures on intermediate-small
cosmological scales. This lack of power may be expressed through
different cosmological parameters in a degenerate manner. In this talk,
after a brief overview of WL and Redshift Space Distortion (RSD), I
will present an updated and extended compilation of growth rate data
based on recent RSD measurements and use it to test its consistency
with the best fit Planck15/LCDM.
Mapas de Galaxias Modernos, Espectros de Potencias de Galaxias y Forecast
Ponente: Miguel Aparicio
Resco
Filiación:
Universidad Complutense de Madrid
Resumen:
La
cosmología, entendida como rama de la física moderna, cuenta con tan
solo cien años de historia desde su fundación en el contexto de la
Teoría General de la Relatividad. Desde entonces las observaciones han
ido aumentando a un ritmo vertiginoso, convirtiendo a la cosmología en
una ciencia de precisión. Los últimos satélites encargados de medir el
fondo cósmico de microondas, WMAP y Planck, así como el análisis de
Supernovas Ia, nos han permitido conocer con precisión la composición
del universo. Dicha composición requiere del enigmático fluido conocido
como energía oscura, cuya dinámica es desconocida. Sin embargo, en los
próximos años, las nuevas generaciones de mapas de galaxias (EUCLID,
DESI, J-PAS…) nos permitirán conocer mucho más acerca de la energía
oscura. En esta charla se presentarán distintos mapas de galaxias. Se
expondrán varios efectos observables en los mapas de galaxias que
dependen del modelo cosmológico. Y finalmente, concluiremos con las
técnicas para estimar errores en los parámetros cosmológicos.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Gravity at the horizon: new probes of gravity and cosmic acceleration
Ponente: Miguel
Zumalacarregui
Filiación:
Nordita/UC Berkeley
Resumen:
Gravity is
core to many unsolved problems in physics, including the properties of
black holes, the nature of space-time and the origin of the universe.
The desire to better comprehend gravity and the mounting evidence for
cosmic acceleration have led to the proliferation of both alternatives
to Einstein's theory and efforts to test them. I will present recent
progress to understand these theories and determine the properties of
gravity using gravitational waves and the large scale structure of the
universe: The speed of gravitational waves will provide the most
stringent test for a large class of theories, while a new generation of
galaxy surveys will be sensitive to new relativistic effects on the
largest cosmological scales. I will also introduce /hi_class/ (www.hiclass-code.net), an
accurate, fast and flexible code to compute cosmological predictions in
a very large class of gravitational theories.
Relaciones universales I-LOVE-QNM para modos cuasi-normales de estrellas de neutrones que contienen materia exótica
Ponente: Luis Manuel
González Romero
Filiación:
Universidad Complutense de Madrid
Resumen:
Se analizará
el espectro de modos cuasi-normales de modelos realistas de estrellas
de neutrones estudiando los modos axiales y polares. Consideraremos
diferentes ecuaciones de estado que satisfacen la ligadura de 2 masas
solares, la mayor parte de ellas conteniendo materia exótica. Se
presentarán relaciones fenomenológicas nuevas entre la frecuencia y el
tiempo de amortiguamiento de los modos. Estas nuevas relaciones son
independientes de la ecuación de estado y relacionan el espectro de
modos cuasi-normales con propiedades globales de la estrella. También,
se presentarán relaciones universales entre las propiedades de los
modos cuasi-normales y los parámetros I-LOVE-Q de estos modelos de
estrellas de neutrones.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Gran explosión, constante cosmológica y gravedad cuántica: maravillas del siglo
Ponente: Gianluca Calcagni
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
Tres
cuestiones han caracterizado la física moderna de las últimas décadas.
La primera es si singularidades tales como las de dentro de los
agujeros negros o la Gran Explosión inicial que dio origen al cosmos se
pueden resolver. La segunda es sobre la determinación de la verdadera
naturaleza de la componente principal y más misteriosa del Universo, la
llamada energía oscura o constante cosmológica. Ni el problema de la
Gran Explosión ni el de la constante cosmológica se pueden acomodar en
la relatividad general de Einstein o en modelos ordinarios de
interacciones de partículas. Una posibilidad es que dichos problemas se
puedan resolver unificando física cuántica y gravitación, pero es muy
difícil formular una teoría y verificarla experimentalmente. Así, la
tercera cuestión es cómo cuantizar la gravedad y extraer predicciones
observables. En esta charla introduciremos estos temas de forma
accesible a un público general.
Primordial perturbations in Hybrid (Loop) Quantum Cosmology
Ponente: Laura Castelló
Gomar
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
A lot of
attention has been devoted recently to the consideration of quantum
corrections to the power spectrum of primordial fluctuations, as a
possible fundamental window on the Early Universe to explore quantum
geometry phenomena. We present a framework for the quantum description
of the evolution of cosmological scalar perturbations, starting from a
formalism designed to preserve covariance, which allows us to extract
physical predictions for those quantum modifications. We show how a
Born-Oppenheimer ansatz leads to the recovery of a Mukhanov-Sasaki
equation in which the coefficients are provided by expectation values
on the background geometry. We also discuss technical tools and develop
a procedure to deal with these quantum corrections beyond the most
direct approximations. The case of hybrid Loop Quantum Cosmology is
commented here. However, the presented scheme is general and aims at
increasing the ability to discriminate between the predictions of
different quantization proposals for cosmological perturbations.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Unruh-deWitt detectors: The Unruh effect and beyond
Ponente: José de Ramón
Rivera
Filiación:
Universidad Complutense de Madrid
Resumen:
The Unruh
deWitt model describes particle detectors. These are two-level quantum
systems in motion along certain space-time trajectories and coupled to
quantum fields. This model is able to describe the so called Unruh
effect: accelerated observers interact with the vacuum of a quantum
field as if they were immersed in a thermal bath with a temperature
proportional to its acceleration. We will discuss some aspects of this
effect, unraveling the notion of thermal equilibrium for quantum fields
and making use of the so called KMS (Kubo-Martin-Schwinger)
condition.Moreover, we will see that the Unruh effect is not the end of
the story, because in many scenarios some peculiarities of particle
detectors are decisive, for instance the switching process, or the
introduction of more than one detector. We will discuss some recent
discoveries as well. We will study how thermalization takes place,
looking for a thermalization time scale. Finally we will discuss when
the monotonic behavior with “temperature” can be lost, inquiring into
the counterintuitive, not well-understood yet Anti-Unruh effect.
Low-energy effects in super-renormalizable gravity models
Ponente: Breno Loureiro
Giacchini
Filiación: Centro
Brasileiro de Pesquisas Físicas, Brasil
Resumen:
Local
gravitational theories with more than four derivatives have remarkable
quantum properties. Namely, they are super-renormalizable and may be
unitary in the Lee-Wick sense, if the massive poles of the propagator
are complex. It is important, therefore, to explore also the IR limit
of these theories and identify observable signatures of the higher
derivatives. In this talk we present recent results in this direction.
Specifically, we discuss the viability of a gravitational seesaw-like
mechanism, which could be a mean of avoiding the Planck suppression of
the higher derivatives' effects. Also, we show that the modified
Newtonian potential in these theories is always a real quantity,
besides being regular at the origin, even if complex poles are allowed
in the propagator. Finally, we consider the bending of light within the
general six-derivative model and discuss the possibility of the
experimental detection of higher derivatives through a
frequency-dependent gravitational scattering.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Loops for dummies
Ponente: Guillermo A. Mena
Marugán
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC)
Resumen:
La Gravedad
Cuántica de Lazos ("Loop Quantum Gravity" en inglés) es uno de los
formalismos más sólidos como candidato para proporcionar una
cuantización consistente de la Relativad General. Su aplicación a
modelos que describen el origen y evolución del Universo ha dado lugar
a una nueva disciplina física conocida como Cosmología Cuántica de
Lazos. Su desarrollo está cambiando de raíz la visión que teníamos del
Cosmos. En este coloquio comentaremos las ideas fundamentales en las
que se basan la Gravedad y la Cosmología Cuántica de Lazos, y
presentaremos en un tono informal (acorde a la filosofía de los "talks
for dummies") algunos de sus avances más importantes.
Playing with the Misner space and the topology
Ponente: Juan Margalef
Bentabol
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Universidad Carlos
III de Madrid
Resumen:
Topology is
essential in many branches of mathematics, however, in physics, it is
often taken for granted as it usually plays no crucial role. I will try
to show that on some cases topology turns out to be essential in order
to understand some pathological behaviors that arise in general
relativity. Namely I will talk about the so-called Misner space, which
shows extremely pathological behaviors that can be neatly understood
through topology. Besides I will introduce the g-boundary, a
topological construction introduced by Hawking and Geroch in an attempt
to define properly what a singularity is, and I will prove that in the
case of the Misner space, one obtains the expected g-boundary.
Spontaneous symmetry breaking and the Unruh effect
Ponente: Antonio Dobado
Filiación:
Universidad Complutense de Madrid
Resumen:
In this work
we consider the ontological status of the Unruh effect. Is it just a
formal mathematical result? Or the temperature detected by an
accelerating observer can lead to real physical effects such as phase
transitions? In order to clarify this issue we use the Thermalization
Theorem to explore the possibility of having a restoration of the
symmetry in a system with spontaneous symmetry breaking of an internal
continuous symmetry as seen by an accelerating observer. We conclude
that the Unruh effect is an ontic effect rather than an epistemic one,
giving rise, in the particular example considered here, to a phase
transition (symmetry restoration) both for global and gauge symmetries
(inverse Higgs mechanism) in the region close to the accelerating
observer horizon.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
What model-independent reconstruction techniques really say about extended theories of gravity
Ponente: Álvaro de la
Cruz-Dombriz
Filiación:
Cosmology and Gravity Group, University of Cape Town and National
Institute for Theoretical Physics (NITheP)
Resumen:
Model
independent techniques are crucial to test both the present ΛCDM
cosmological paradigm and alternative theories making the least
possible number of assumptions about the Universe. Whether cosmography
is able to distinguish between different gravitational theories or not
has remained so far an open question. I will present the bounds on
model parameters for three different extensions of General Relativity,
namely quintessence, F(Torsion) and f(R) theories. Using extensive data
from the Union2.1 SN catalogue, BAO data and H(z) differential age
compilations, and through a Monte Carlo analysis using a
Metropolis-Hastings algorithm with a Gelman-Rubin convergence criterion
this technique is shown to be capable of providing 1-σ and 2-σ
constraints. I shall compare these results to the truncated ΛCDM
paradigm, showing that the permitted regions of coefficients are
significantly modified and in general widened compared to values
reported in the existing literature. Finally Bayesian selection
criteria AIC and BIC will provide further insight on the limitations of
the method.
Didáctica de Materia Oscura
Ponente: José A. R.
Cembranos
Filiación:
Universidad Complutense de Madrid
Resumen:
De acuerdo
con las observaciones actuales, la componente más abundante de la
materia en el universo no se encuentra entre las partículas que
conocemos dentro del modelo estándar de partículas e interacciones
fundamentales. Este nuevo tipo de materia se conoce como materia
oscura. Existen numerosas evidencias de su existencia, sin embargo, no
se ha detectado a través de ningún proceso más allá de sus efectos
gravitacionales. Por ello, la naturaleza de la materia oscura y sus
características fundamentales continúan siendo un misterio, una de las
cuestiones abiertas más importantes dentro de la física actual.
Indirect searches of TeV Dark Matter at the Galactic Center
Ponente: Viviana Gammaldi
Filiación: SISSA,
Italia
Resumen:
I will
discuss several aspects of the indirect search of Dark Matter (DM) at
the Galactic Center (GC). I will show that the gamma-ray flux observed
by HESS from the J1745-290 GC source is well fitted as the secondary
gamma-rays photons generated from DM annihilating into Standard Model
particles in combination with a simple power-law background. The model
independent fits are performed for all the possible channels of
annihilation. The best fits are obtained for WIMP masses above ∼ 10
TeV. They require an enhancement factor of ∼ 10^3 and a background
spectral index compatible with the Fermi-LAT data. I will investigate
the possibility that the expected enhancement may be related with
hydrodynamics in N-body simulation or a possible DM spike induced by
the Super Massive Black Hole. I will also discuss the possibility that
the latter could be related with the spatial tail detected in the
gamma-ray signal by HESS II in 2015. These TeV DM masses are
practically unconstrained by direct detection searches or colliders
experiments, but they can be tested with the observations of other
cosmic-rays.
Observational imprints of the interacting multiverse
Ponente: Salvador Robles
Pérez
Filiación: Estación
Ecológica de Biocosmología
Resumen:
The most
controversial feature of the multiverse may be its testability. We
present a novel paradigm of the multiverse where non-local interactions
and other quantum correlations may exist among the universes of the
multiverse. The interactions among universes may: i) determine some
global properties of a single universe without violating its notion of
causal closure; ii) produce a landscape structure of vacuum states that
might lead to different process of vacuum decay; and iii) induce a
pre-inflationary stage in the evolution of the universe that cannot be
reproduced by any known matter content. All these effects would leave
distinctive and distinguishable imprints in the properties of the CMB,
making the whole proposal (and the underlying theories) testable.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Unitary dynamics selecting a quantization of the Dirac field in cosmology
Ponente: Beatriz Elizaga
de Navascués
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
It is well
known that linear canonical transformations are not generally
implemented as unitary operators in QFT. Such transformations include
the dynamics that arises from linear field equations on the background
spacetime. This evolution is specially relevant in nonstationary
backgrounds, where there is no time-translational symmetry that can be
exploited to select a quantum theory. We investigate whether it is
possible to find a Fock representation for the canonical
anticommutation relations of a Dirac field, propagating on a
homogeneous and isotropic cosmological background, such that the field
evolution is unitarily implementable. First, we restrict our attention
to Fock representations that are invariant under the group of spatial
isometries of the background. Then, we prove that there indeed exist
Fock representations such that the dynamics is implementable as a
unitary operator. Finally, once a convention for the notion of
particles and antiparticles is set, we show that these representations
are all unitarily equivalent.
Late-time cosmology in f(R) gravity
Ponente: João Morais
Filiación: UPV
Resumen:
Since the
discovery of the current acceleration of the Universe by the Supernova
Cosmology Project and the High-Z Supernova Search Team in 1998, several
proposals have been put forward to explain the nature of the dark
energy fluid that governs such late-time behaviour. Among these
different proposals, the modified theories of gravity, which have since
then been the focus of a renewed interest, try to obtain the late-time
acceleration through modifications of the Einstein-Hilbert action. In
this talk, we will focus on metric f(R) theories of gravity, a
particular class of modified theories of gravity, which replace the
Ricci scalar R in the action by a general function f(R). In a first
step we review the "designer" or "reconstruction" approach, which tries
to derive viable f(R) actions from cosmological models. We apply this
methodology to the modified Generalized Chaplygin Gas and obtain the
compatible f(R). This model is constrained, using the latest Planck
2015 data, within the cosmographic approach and through the computation
of the effects on the matter power spectrum as observed today. The
matter power spectrum is computed using the full theory of linear
perturbations for metric f(R) theories without any approximation in the
perturbed equations.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Spacetime-noncommutativity regime of Loop Quantum Gravity
Ponente: Michele Ronco
Filiación:
Universidad de Roma - La Sapienza, Italia
Resumen:
A recent
study by Bojowald and Paily provided a path toward the identication of
an effective quantum-spacetime picture of Loop Quantum Gravity,
applicable in the "Minkowski regime", the regime where the large-scale
(coarse-grained) spacetime metric is flat.
A pivotal role in the analysis is played by Loop-Quantum-Gravity-based modications to the hypersurface deformation algebra, which leave a trace in the Minkowski regime. We here show that the symmetry-algebra results reported by Bojowald and Paily are consistent with a description of spacetime in the Minkowski regime given in terms of the kappa-Minkowski noncommutative spacetime, whose relevance for the study of the quantum-gravity problem had already been proposed for independent reasons.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Hamiltonian formulation of parametrized field theories: incorporating boundaries and gauge symmetries
Ponente: Fernando Barbero
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
Parametrized
field theories have been used as a test bed for polymer quantization
techniques in Loop Quantum Gravity. In this talk I will review the
Hamiltonian formulation for singular (constrained) systems and discuss
several issues that play a relevant role in the Hamiltonian description
of parametrized models when boundaries and internal gauge symmetries
are present. For concreteness I will concentrate on the discussion of
the scalar field subject to several types of boundary conditions and
electromagnetism.
Quantum corrections to the Higgs potential on a curved background
Ponente: Franco D. Albareti
Filiación:
Universidad Autónoma de Madrid
Resumen:
I will
present recent results on finite gravitational corrections to the Higgs
effective potential. In particular, 1-loop corrections due to the Higgs
self-interactions are computed in a perturbed FRW background by mode
summation. For this aim, the Klein-Gordon equation is solved to first
order in perturbations and to zero order in the adiabatic
approximation.
Dimensional regularization techniques are used to compute not only the divergent parts of the effective potential but also the finite ones. The obtained results amount to the presence of inhomogeneities in the Higgs vacuum expectation value which translate into variations on the masses of elementary particles. Possible observable signatures within the Solar System and on cosmological scales will be discussed.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Einstein-Yang-Mills-Lorentz Black Holes
Ponente: Jorge Gigante
Valcárcel
Filiación:
Universidad Complutense de Madrid
Resumen:
Since the
discovery of the first non-abelian solution to the Einstein-Yang-Mills
(EYM) theory done by Bartnik and McKinnon, a large number of properties
and different solutions have been obtained. As they manifestly violate
the non-hair conjecture, they have attracted much attention and
encouraged a deep search for other black hole geometries.
In this talk, first we will review the most relevant particle-like and black hole solutions for such a theory. In addition, we will focus on the EYM-SO(N) model and establish a particular equivalence between this case and a certain class of theories with torsion within Riemann-Cartan space-times, in order to simplify the problem of finding exact solutions to the EYM equations. Finally, solutions for the torsion-free and the non-vanishing torsion with rotation and reflection symmetries will be presented by the explicit use of this method.
Clasificación completa de singularidades cosmológicas
Ponente: Leonardo
Fernández-Jambrina
Filiación:
Universidad Politécnica de Madrid
Resumen:
El
descubrimiento de la expansión acelerada del universo ha motivado la
consideración de singularidades cosmológicas más allá de los clásicos
Big Bang y Big Crunch. La primera de ellas fue el Big Rip, pero, a
medida que se han ido proponiendo nuevos modelos, han ido apareciendo
muchas más posibilidades. Incluso se están proponiendo nuevos
escenarios no singulares como estado final posible para el Universo,
tales como el Little Big Rip o el Pseudorip.
En esta charla se propondrá un intento sistemático de derivar todas estas familias de singularidades y escenarios, y algunas nuevas más, a partir de desarrollos en serie generalizados del parámetro de deceleración del universo o del índice barotrópico y se relacionará con resultados anteriores para determinar la fuerza de estas singularidades, ya que en muchos caso son débiles y no podrían considerarse un final para el universo.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Fast oscillating fields cosmology
Ponente: Santos J. Núñez
Jareño
Filiación:
Universidad Complutense de Madrid
Resumen:
The ubiquity
of scalar fields in cosmology is not only owed to its simplicity, but
mainly because it intrinsically respects the large degree of isotropy
observed in the universe. On the contrary, the evolution of a coherent
vector field is clearly anisotropic. However, we will show that the
energy-momentum tensor of homogeneous fields of arbitrary spin in an
expanding universe is always isotropic in average provided the fields
remain bounded and evolve rapidly compared to the rate of expansion.
This property enlarge the plausible candidates to solve cosmological
problems to higher spin theories.
In the second part of the talk we will discuss the perturbations of a fast oscillating scalar field under a power law potential, following an effective approach as well as the exact system solution in the sub/super-Hubble limits.
Colapso de materia cuántica autogravitante sobre una geometría cuántica
Ponente: Javier Olmedo
Filiación:
Universidad Estatal de Luisiana
Resumen:
En esta
charla voy a resumir los últimos avances en relación a la cuantización
de espacio-tiempos esféricamente simétricos en gravedad cúantica de
lazos. Resumiré brevemente el escenario en ausencia de materia.
Después, consideraré el acoplo con una cáscara autogravitante, fina,
esférica y sin masa. Introduciré una redefinición del álgebra de
ligaduras de tal modo que la ligadura escalar conmute consigo misma.
Mostraré que esto se puede llevar a cabo también en el nivel cuántico.
Además proporcionaré los observables cuánticos del modelo y definiré
las componentes de la métrica a partir de ellos como observables
parametrizados. Finalmente discutiré las consecuencias físicas.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Is Cosmography a useful tool to target extended theories of gravity?
Ponente: Álvaro de la
Cruz-Dombriz
Filiación:
Universidad Complutense de Madrid
Resumen:
Model-independent methods in cosmology have become an essential tool in
order to deal with an increasing number of theoretical alternatives for
explaining the late-time acceleration of the Universe. In principle,
this provides a way of testing the Cosmological Concordance model under
different assumptions and to rule out whole classes of competing
theories. One such model-independent method is the so-called
cosmographic approach, which relies only in the homogeneity and
isotropy of the Universe on large scales. We show that this method
suffers from many shortcomings, providing biased results depending on
the auxiliary variable used in the series expansion and is unable to
rule out models or adequately reconstruct theories with higher-order
derivatives in either the gravitational or matter sector. Consequently,
in its present form, this method seems unable to provide reliable or
useful results for cosmological applications.
Higher derivative actions and inflation in string theory
Ponente: Francisco Pedro
Filiación:
Instituto de Física Teórica (IFT-CSIC), Madrid
Resumen:
In this talk
I will explore some aspects of higher derivative (>2) supergravity
actions. I will review how the vacua and scalar potential of the
bosonic sector of type IIB string compactifications can get modified in
the presence of such corrections and will use them to build a viable
inflationary model, where the inflaton is a geometric modulus,
parametrising the size of the compactification space.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Phase Space Noncommutativity: From Gravity to Quantum Mechanics
Ponente: Catarina Bastos
Filiación:
Instituto Superior Técnico (IST), Lisboa
Resumen:
A phase-space
noncommutativity (NC) is considered in the context of a Kantowski-Sachs
cosmological model. Then, the interior of a Schwarzschild black hole is
analyzed. One deduces the thermodynamics and show that the Hawking
temperature and entropy exhibit an explicit dependence on the momentum
noncommutativity parameter, η. Furthermore, the t=r=0 singularity is
analysed in the noncommutative regime and it is shown that the wave
function vanishes in this limit.
Quantumness and separability criteria for continuous variable systems are discussed for the case of a NC phase-space quantum mechanics. In particular, the quantum nature and the entanglement configuration of NC two-mode Gaussian states are examined. Finally, a more general measurement disturbance uncertainty principle is presented in a Robertson-Schrödinger formulation. It is shown that it is stronger and having nicer properties than Ozawa’s uncertainty relations. In particular is invariant under symplectic transformations. One shows also that there are states of the probe (measuring device) that saturate the matrix formulation of measurement disturbance uncertainty principle.
Aplicaciones del grafeno en física fundamental. Renormalización, campos gauge y curvatura con fermiones de Dirac sin masa en dos dimensiones
Ponente: José González
Carmona
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
El
descubrimiento del grafeno ha supuesto toda una revolución, no solo por
el considerable potencial de este material para aplicaciones
tecnológicas, sino también por ofrecer un banco de pruebas donde
experimentar con una gran variedad de fenómenos de física fundamental.
En esta charla repasaremos algunos de los efectos que derivan del comportamiento de las excitaciones electrónicas del grafeno como fermiones de Dirac sin masa, haciendo énfasis en cómo el grado de libertad adicional (pseudoespín) de las excitaciones conduce a signaturas no convencionales que se pueden medir en el sistema electrónico.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Sistema de dos niveles en las cercanías de un agujero negro de Schwarzschild
Ponente: Jose Sánchez
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
La búsqueda
de agujeros negros no es tarea fácil. Mediante el estudio del espectro
de emisión espontánea de un sistema de dos niveles, se propone una
posibilidad para la misma. Se discuten aspectos básicos de la
cuantización de campos cuando consideramos espacio tiempos no planos y
se discuten algunos de los efectos derivados. Igualmente se discuten
los aspecto básicos de la óptica cuántica para sistemas de dos niveles,
llegando a la llamada ecuación maestra.
Effective field theory approach to modified gravity with applications to inflation and dark energy
Ponente: Shinji Tsujikawa
Filiación: Tokyo
University of Science, Japón
Fecha y hora:
Lugar: Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Sparsity of the Hawking flux
Ponente: Matt Visser
Filiación: Victoria
University of Wellington, New Zealand
Resumen:
The Hawking
flux that reaches spatial infinity is extremely sparse and thin, with
the Hawking quanta dribbling out of the black hole one-by-one. The
typical time between quanta reaching infinity is larger than the
timescale set by the energy of the quanta by factors of many hundreds.
Among other things, this means that the Hawking evaporation of a black
hole should be viewed as a sequential cascade of 3-body decays.
Constraining the early universe with primordial black holes
Ponente: Sam Young
Filiación: Dept. of
Physics and Astronomy, University of Sussex, Reino Unido
Resumen:
Primordial
black holes (PBHs) could have formed very early in the history of the
universe after inflation ended. They are a viable dark matter candidate
and represent a unique probe to study the small scales of the early
universe, not visible by other means. I will discuss how PBHs have been
used to constrain the small scales, and how this depends strongly on
the non-Gaussianity parameters, as well as how PBHs can be used to
constrain the large scales in the early universe.
“The magnificent seven and friends”: Horndeski theories self-tuning to de Sitter
Ponente: Prado Martín
Moruno
Filiación:
Universidad Complutense de Madrid
Resumen:
The
cosmological constant problem is not alleviated in the context of
alternative theories of gravity generically. Focusing attention on
theories with equations containing non-higher than second order
derivatives, Horndeski theories, there is a dynamical adjustment
mechanism able to screen any value of the cosmological constant. Under
the assumption that the gravity's vacuum is described by a de Sitter
geometry, the late time accelerated expansion of the universe can be
understood as the result of that adjustment mechanism. I will present
the Horndeski models able to carry out that kind of screening, which,
therefore, have a de Sitter critical point for any type of material
content. I will summarize the cosmological consequences of the
resulting models, emphasizing the case with symmetry under shift
redefinitions of the field.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Non-linear evolution of the BAO scale in alternative theories of gravity
Ponente: Miguel
Zumalacárregui
Filiación: ITP
Heidelberg/Nordita
Resumen:
The scale of
Baryon Acoustic Oscillations (BAO) imprinted in the matter distribution
is known to suffer sub-percent deviations from being a perfect standard
ruler due to non-linear corrections. However, such corrections have
never been computed in alternative theories of gravity. I will give an
overview of historical and recent developments in alternative theories
of gravity and present the first computation of the BAO shift based on
perturbation theory (à la Bellini-Sawicki) and a peak-background split
(à la Sherwin-Zaldarriaga), valid for any Horndeski theory. The BAO
shift is modified by the enhanced growth of linear perturbations, as
well as by novel, non-linear gravitational effects. The modified
gravity result can range from a negligible to order-unity correction at
z=0 depending on the model, and in some cases presents a characteristic
time evolution. Although small, this effect might be within the reach
of future galaxy surveys, and might have implications for BAO
reconstruction in theories other than Einstein's.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Quantum cosmology: Games without frontiers
Ponente: Ana Alonso Serrano
Filiación:
Instituto de Física Fundamental (IFF-CSIC), Madrid
Resumen:
In classical
General Relativity, the presence of horizons excises parts of the
spacetime making inaccessible physical observations beyond them. But,
is it so quantum mechanically? We develop a canonical quantization of a
minisuperspace model whose classical solutions possess horizons, in
order to check that this is not the case: Quantum gravitational states
with support in spacetime configurations that exclusively describe
either each region of the whole spacetime are not consistent, due to
quantum correlations that appear across the horizon, making the
physical states of the different regions not separable but entangle.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Modifying General Relativity: is it worth?
Ponente: Diego Sáez-Gómez
Filiación: U. of
Lisbon and ACGC - U. of Cape Town
Resumen:
In this talk
I will review some models of modified gravities and their features from
a classical point of view. Over the last years, modified gravities have
drawn much attention within the cosmological context since they can
reproduce with great accuracy the late-time acceleration and even the
inflationary epoch. I will show the pros and cons of some of the main
proposals.
Graphene: Dirac fermions in curved spaces
Ponente: Alberto Cortijo
Filiación:
Instituto de Ciencia de Materiales de Madrid, CSIC
Resumen:
It is well
known that the low energy electronic excitations in graphene are
described by the massless Dirac equation. It might seem natural in
terms of effective field theories that when a graphene sheet is
corrugated the description in terms of Dirac fermions can still be
valid, but in a curved background. In this seminar we review the
consequences of assuming such viewpoint and we compare it with the
usual approach adopted in solid state physics.
Anomaly-induced effective action and Starobinsky model of inflation
Ponente: Ilya L. Shapiro
Filiación:
Universidade Federal de Juiz de Fora, Brasil
Resumen: The effective action of gravity contains the main information about quantum effects, but in most cases it can not be calculated exactly. An important exception is the one-loop effective action for massless conformal invariant matter fields, which can be obtained by integrating trace anomaly. The integration constant is an arbitrary conformal functional of the background metric, but for the zero-order cosmology this functional is irrelevant and the solution becomes exact. The most important applications include systematic classification of vacuum states in the vicinity of the black hole and the Starobinsky model of inflation. The last is based on the non-local anomaly-induced metric, however the most relevant part is a local term which is just a square of the scalar curvature. The modified version of the model does not require special choice of initial conditions and is based on the interpolation between stable and unstable inflationary solutions.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
A bridge between the microscopic structure of space-time and effective geometries: the crystal lessons
Ponente: Diego
Rubiera-Garcia
Filiación:
Universidad de Fudan, Shanghái, China
Resumen: A striking mathematical and physical resemblance exists between quantum gravity effective geometries arising from a hypothetical microstructure of space-time pervaded by creation and annihilation of wormholes (space-time foam), and the continuized version of crystalline structures. If the latter contains defects on its microstructure, the macroscopic effective description must be done in terms of a metric-affine geometry with nonmetricity and torsion. Using a crystal-motivated action in a simplified scenario, we find the presence of Wheeler's geons: self-consistent topologically non-trivial gravito-electromagnetic entities, representing the gravitional analog of point defects.
What lessons can we extract from this analogy?
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
CMB: beyond the standard statistical scenario
Ponente: Thiago Dos Santos
Pereira
Filiación:
Universidade Estadual de Londrina, Brasil
Resumen: In this talk I will review the basic hypotheses which motivate the statistical framework used to analyze the cosmic microwave background radiation (CMB), and discuss how that framework can be enlarged as we relax those hypotheses. In particular, I will try to separate as much as possible the questions of gaussianity, homogeneity and isotropy from each other, while giving particular emphasis to their signatures and the enhanced "cosmic variances" that become increasingly important as our putative Universe becomes less symmetric. After reviewing the basic formalism I will present a few model-independent statistical tests, including some new results, which can be applied to CMB data when searching for large scale “anomalies”.
Fecha
y hora:
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Topological Quantum Computation - From Concepts To Experiment
Ponente: Markus Müller
Filiación: Dpto. de
Física Teórica I, Universidad Complutense de Madrid.
Resumen: Quantum computers hold the promise to allow one to solve problems that cannot be efficiently treated on classical computers. To date, the construction of a quantum computer remains a fundamental scientific and technological challenge, due the influence of unavoidable noise which affects the fragile quantum states.
In our talk, we begin with a general introduction to quantum computation and then introduce the basic idea of quantum error correction based on topological quantum codes, which allow one to protect quantum information during storage and processing. We then discuss a recent experimental realization of a quantum error correcting code in which a logical qubit was distributed over seven trapped-ion qubits. This encoding not only allowed us to detect arbitrary single-qubit errors, but also to realize for the first time quantum computations on an encoded qubit. This quantum error correcting code represents a fully functional instance of a topologically encoded qubit, or color code, and opens a route toward fault-tolerant quantum computing.Fecha
y hora:
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
Vacuum energy (again), but now it seems dark matter
Ponente: Franco D. Albareti
Filiación:
Instituto de Física Teórica (IFT-CSIC/UAM)
Resumen: A comoving cutoff is used to renormalize the vacuum stress-energy tensor of a scalar field in RW geometries in a covariant way. At the IR regime (late times) a matter-like contribution dominates. A phenomenological bound to the comoving cutoff is obtained from the current abundance of dark matter. It is also shown that this "dark matter" could support perturbations with a negligible speed of sound, thus it could seed the formation of structures.
Besides, I will present the latest results on the possible variation of the fine structure constant using SDSS-III/BOSS QSO spectra with [OIII] emission lines.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Supernovae as probes of cosmic parameters: estimating the bias from under-dense lines of sight
Ponente: Vinicius Busti
Filiación: Centro
de Astrofísica, Cosmología y Gravedad, Universidad de Ciudad del Cabo,
Sudáfrica
Resumen: Correctly interpreting observations of sources such as type Ia supernovae (SNe Ia) require knowledge of the power spectrum of matter on AU scales—which is very hard to model accurately. Because under-dense regions account for much of the volume of the universe, light from a typical source probes a mean density significantly below the cosmic mean. The relative sparsity of sources implies that there could be a significant bias when inferring distances of SNe Ia, and consequently a bias in cosmological parameter estimation. While the weak lensing approximation should in principle give the correct prediction for this, linear perturbation theory predicts an effectively infinite variance in the convergence for ultra-narrow beams.
In this talk, I will adopt an observational viewpoint and discuss some approximations to see the effects of under-dense lines of sight might have in parameter estimation. Also, I will address tests to decide what is the best way to describe light propagation in the real Universe.
Fecha
y hora:
Lugar: CSIC, CFMAC, sala de
conferencias (c/ Serrano,
121)
The cosmological constant problem: a lesson from Helium-3
Ponente: Gil Jannes
Filiación:
Universidad Carlos III de Madrid
Resumen:
The
effective gravity emerging for relativistic quasiparticles in
superfluid 3He-A provides a direct connection between the properly
determined vacuum energy and the cosmological constant lambda. This
connection is non-trivial, and requires a detour via the masses of the
‘gravitons’ in the associated bi-metric gravity. Although the
cosmological constant lambda turns out to be huge—it is determined by
the effective Planck scale—, the cosmological term (the stress-energy
tensor associated to lambda) is in fact naturally non-constant and
vanishes in the equilibrium vacuum, as dictated by thermodynamics. This
suggests that the equilibrium state of any condensed-matter system, and
perhaps also the final state of the Universe, is not gravitating.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Junction conditions in gravity theories
Ponente: José M. M.
Senovilla
Filiación:
Universidad del País Vasco (UPV/EHU), Bilbao
Resumen: I will present the method to obtain the proper junction conditions in general theories of gravity, highlighting the differences specific to General Relativity (GR) and its peculiarities. As an illustrative example I will consider F(R) Lagrangian theories explicitly.
The discussion will analyze two different junction levels: allowing for branes/thin shells or not. In the former case I will argue that the generic brane/shell construction is crucially different to that in GR. In the latter case I will show that properly matched solutions in GR are no longer solutions of F(R—and other—theories.
(An exceptional case arises in theories with a Lagrangian quadratic in the curvature: gravitational double layers are feasible, and this leads to new Physics—but I will probably have no time to describe this)
Fecha
y hora:
Lugar:
CSIC,
CFMAC,
sala de
conferencias (c/ Serrano,
121)
Cosmología y gravedad cuántica
Ponente: Gianluca Calcagni
Filiación:
Instituto de Estructura de la Materia (IEM-CSIC), Madrid
Resumen:
Se revisan
los problemas cosmológicos de la Gran Explosión (¿El universo nació de
una singularidad inicial como predice la relatividad clásica?) y de la
energía oscura (¿Por qué el universo reciente está acelerando?) en
algunos enfoques de gravedad cuántica y teorías que van más allá del
Modelo Estándar. Aunque no haya todavía ninguna solución consolidada y
satisfactoria de ambos problemas, las observaciones cosmológicas
modernas pueden proporcionar una valiosa información sobre diversos
modelos exóticos de física de partículas y de gravedad.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Averaging and modified gravity theories: An overview of tools able to explain the cosmological late-time acceleration
Ponente: Álvaro de la Cruz
Dombriz
Filiación:
Universidad Complutense de Madrid
Resumen:
One
possible explanation for the present observed acceleration of the
Universe is the breakdown of homogeneity and isotropy due to the
formation of non-linear structures. How the formation of non-linear
structures and subsequent inhomogeneities affect the averaged
cosmological expansion rate and may eventually lead to late-time
acceleration is usually referred to as backreaction mechanism. General
Relativity together with dust matter scenarios have until recently been
considered as the sole ingredients for averaged calculations. We shall
present the backreaction formalism in more general scenarios, including
imperfect fluids as well as extended theories of gravity, and apply an
averaging procedure to them in order to determine possible backreaction
effects.
Cosmological solutions in bigravity
Ponente: Prado
Martín-Moruno
Filiación:
Instituto Superior Técnico, Lisboa, Portugal
Resumen:
Bigravity
theories, which are formulated using two mutually interacting dynamical
metrics, were initially introduced by Isham, Salam, and Strathdee in
the seventies. These theories have recently attracted considerable
attention since Hassan and Rosen found a bigravity theory which is
potentially stable, that is, free of the Boulware–Deser ghost which
otherwise affects these theories. As bigravity can be interpreted to
describe two different universes, I will present a simple way to study
the cosmology of such a classical bi-universe in general situations. I
will pay particular attention to the interplay of both gravitational
sectors and how one can extract conclusions about the dynamics of one
universe from the knowledge about the occurrence of violent events in
the other universe.
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Emergent electromagnetism: some training towards a theory of emergent gravity
Ponente: Carlos Barceló
Filiación:
Instituto de Astrofísica de Andalucía (IAA-CSIC), Granada
Fecha
y hora:
Lugar:
Facultad de Ciencias Físicas
de la UCM,
Dpto. de Física Teórica I, sala de seminarios (3.ª planta)
Contacta con el
webmaster
