## Past seminars

### Loop gravity without spin networks

Abstract: 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.

### Taming the beast: initial conditions and degrees of freedom in non-local gravity

Abstract: 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.

### Towards new constraints in extended theories of gravity: large-scale structures, neutron stars and SKA

Abstract: 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.

### Testing the Dark Universe with Gravitational Waves

Abstract: 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.

### Primordial fluctuations in Loop Quantum Cosmology

Abstract: 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.

### From LISA Pathfinder to LISA: Enabling the Science of the Gravitational-Wave Low-Frequency Band

Abstract: 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.

### Fractional Calculus as a Modelling Framework

Abstract: 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.

### Astrofísica gamma y física fundamental con MAGIC

Abstract: 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.

### Coincident General Relativity

### Computational Complexity and Holography

### Gravitational waves. What's in for hadron physics?

### Forecast and analysis of the cosmological redshift drift

### Early Universe with a Born-Infeld taste

### Lorentz invariance and the zero-point stress-energy

### Properties of Rotating Black Holes in Odd Dimensions

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.

### The smooth and clumpy universe: present and asymptotic behaviour(s)

### Deformed relativistic symmetries: decoherence and dimensional reduction at the Planck scale

### Tension and constraints on modified gravity parametrizations of Geff(z) from growth rate and Planck data

### Mapas de Galaxias Modernos, Espectros de Potencias de Galaxias y Forecast

### Gravity at the horizon: new probes of gravity and cosmic acceleration

*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

### Gran explosión, constante cosmológica y gravedad cuántica: maravillas del siglo

### Primordial perturbations in Hybrid (Loop) Quantum Cosmology

### Unruh-deWitt detectors: The Unruh effect and beyond

### Low-energy effects in super-renormalizable gravity models

### Loops for dummies

### Playing with the Misner space and the topology

### Spontaneous symmetry breaking and the Unruh effect

### What model-independent reconstruction techniques really say about extended theories of gravity

### Didáctica de Materia Oscura

### Indirect searches of TeV Dark Matter at the Galactic Center

### Observational imprints of the interacting multiverse

### Unitary dynamics selecting a quantization of the Dirac field in cosmology

### Late-time cosmology in f(R) gravity

### Spacetime-noncommutativity regime of Loop Quantum Gravity

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.

### Hamiltonian formulation of parametrized field theories: incorporating boundaries and gauge symmetries

### Quantum corrections to the Higgs potential on a curved background

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.

### Einstein-Yang-Mills-Lorentz Black Holes

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

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 podrán considerarse un final para el universo.

### Fast oscillating fields cosmology

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

### Is Cosmography a useful tool to target extended theories of gravity?

### Higher derivative actions and inflation in string theory

### Phase Space Noncommutativity: From Gravity to Quantum Mechanics

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

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.

### Sistema de dos niveles en las cercanías de un agujero negro de Schwarzschild

### Effective field theory approach to modified gravity with applications to inflation and dark energy

### Sparsity of the Hawking flux

### Constraining the early universe with primordial black holes

### "The magnificent seven and friends": Horndeski theories self-tuning to de Sitter

### Non-linear evolution of the BAO scale in alternative theories of gravity

### Quantum cosmology: Games without frontiers

### Modifying General Relativity: is it worth?

### Graphene: Dirac fermions in curved spaces

### Anomaly-induced effective action and Starobinsky model of inflation

Abstract: 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.

### A bridge between the microscopic structure of space-time and effective geometries: the crystal lessons

Abstract: 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?

### CMB: beyond the standard statistical scenario

Abstract: 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".

### Topological Quantum Computation - From Concepts To Experiment

Abstract: 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.### Vacuum energy (again), but now it seems dark matter

Abstract: 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.

### Supernovae as probes of cosmic parameters: estimating the bias from under-dense lines of sight

Abstract: 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.

### The cosmological constant problem: a lesson from Helium-3

### Junction conditions in gravity theories

Abstract: 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)

### Cosmología y gravedad cuántica

### Averaging and modified gravity theories: An overview of tools able to explain the cosmological late-time acceleration

### Cosmological solutions in bigravity

### Emergent electromagnetism: some training towards a theory of emergent gravity

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