## Person: Garay Elizondo, Luis Javier

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##### First Name

Luis Javier

##### Last Name

Garay Elizondo

##### Affiliation

Universidad Complutense de Madrid

##### Faculty / Institute

Ciencias Físicas

##### Department

Física Teórica

##### Area

Física Teórica

##### Identifiers

13 results

## Search Results

Now showing 1 - 10 of 13

Publication Derivative couplings in gravitational production in the early universe(Springer, 2020-09-09) Borrajo Gutierrez, Daniel; Ruiz Cembranos, José Alberto; Garay Elizondo, Luis Javier; Sánchez Velázquez, José ManuelGravitational particle production in the early universe is due to the coupling of matter fields to curvature. This coupling may include derivative terms that modify the kinetic term. The most general first order action contains derivative couplings to the curvature scalar and to the traceless Ricci tensor, which can be dominant in the case of (pseudo-)Nambu-Goldstone bosons or disformal scalars, such as branons. In the presence of these derivative couplings, the density of produced particles for the adiabatic regime in the de Sitter phase (which mimics inflation) is constant in time and decays with the inverse effective mass (which in turn depends on the coupling to the curvature scalar). In the reheating phase following inflation, the presence of derivative couplings to the background curvature modifies in a nontrivial way the gravitational production even in the perturbative regime. We also show that the two couplings - to the curvature scalar and to the traceless Ricci tensor - are drastically different, specially for large masses. In this regime, the production becomes highly sensitive to the former coupling while it becomes independent of the latter.Publication Interpretations and naturalness in the radiation-reaction problem(MDPI, 2021-04-12) Barceló, Carlos; Garay Elizondo, Luis Javier; Redondo Yuste, JaimeAfter more than a century of history, the radiation-reaction problem in classical electrodynamics still surprises and puzzles new generations of researchers. Here, we revise and explain some of the paradoxical issues that one faces when approaching the problem, mostly associated with regimes of uniform proper acceleration. The answers we provide can be found in the literature and are a synthesis of a large body of research. We only present them in a personal way that may help in their understanding. Besides, after the presentation of the standard answers, we motivate and present a twist to those ideas. The physics of emission of radiation by extended charges (charges with internal structure) might proceed in a surprising oscillating fashion. This hypothetical process could open up new research paths and a new take on the equivalence principle.Publication Emergent gauge symmetries: Yang-Mills theory(Springer, 2021-05-02) Barceló, Carlos; Carballo Rubio, Raúl; Garay Elizondo, Luis Javier; García Moreno, GerardoIn this article, subleading (in 1/N) corrections to the action of the one loop dilatation operator in the su(3) sector of N = 4 super Yang-Mills theory are studied. We focus on the system of operators dual to two giant graviton systems, which have a bare dimension ∼ O(N) and are a linear combination of restricted Schur polynomials with p = 2 long columns. At the leading order the dilatation operator gives rise to the free part of an emergent Yang-Mills theory, arising from the open string excitations of the giant gravitons. We verify that the terms we study describe interactions between these open string excitations. The interactions have the U(1)×U(1) gauge invariance expected for a pair of separated branes.Publication Vacuum Semiclassical Gravity Does Not Leave Space for Safe Singularities(MDPI, 2021-08-01) Arrechea, Julio; Barceló, Carlos; Boyanov Savov, Valentin; Garay Elizondo, Luis JavierGeneral relativity predicts its own demise at singularities but also appears to conveniently shield itself from the catastrophic consequences of such singularities, making them safe. For instance, if strong cosmic censorship were ultimately satisfied, spacetime singularities, although present, would not pose any practical problems to predictability. Here, we argue that under semiclassical effects, the situation should be rather different: the potential singularities which could appear in the theory will generically affect predictability, and so one will be forced to analyse whether there is a way to regularise them. For these possible regularisations, the presence and behaviour of matter during gravitational collapse and stabilisation into new structures will play a key role. First, we show that the static semiclassical counterparts to the Schwarzschild and Reissner–Nordström geometries have singularities which are no longer hidden behind horizons. Then, we argue that in dynamical scenarios of formation and evaporation of black holes, we are left with only three possible outcomes which could avoid singularities and eventual predictability issues. We briefly analyse the viability of each one of them within semiclassical gravity and discuss the expected characteristic timescales of their evolution.Publication Analogue gravity simulation of superpositions of spacetimes(Springer, 2022-08-20) Barceló, Carlos; Garay Elizondo, Luis Javier; García Moreno, GerardoTaking the principles of quantum mechanics as they stand and applying them to gravity, leads to the conclusion that one might be able to generate superpositions of spacetimes, at least formally. We analyze such a possibility from an analogue gravity perspective. We present an analogue toy model consisting of a Bose-Einstein condensate in a double-well potential and identify the states that could potentially be interpreted as superposition of effective spacetimes. These states are unstable and the source of instability from a microscopic point of view can be related to the absence of a well-defined causal structure in the effective geometric description. We explore the consequences of these instabilities and argue that they resonate with Penrose's ideas about the decay that superpositions of states with sufficiently different gravitational fields associated should experience.Publication Warp drive aerodynamics(Springer, 2022-08-29) Barceló, Carlos; Boyanov Savov, Valentin; Garay Elizondo, Luis Javier; Martín Martínez, Eduardo; Sánchez Velázquez, José ManuelIn this work we analyse the potential for a warp drive spacetime to develop instabilities due to the presence of quantum matter. Particularly, we look for points of infinite blueshift (which are analogous to points of a black hole inner horizon, known for its semiclassical instability), and categorise them through the behaviour of geodesics in their vicinity. We find that warp-drive bubbles in dimension 2+1 or higher are in fact likely to be stable, as they generally contain only isolated points where divergences are approached, leading to a finite limit for the overall accumulation of destabilising energy. Furthermore, any semiclassical instabilities in the warp drive due to energy-density buildups can be further diminished with particular, more "aerodynamic" shapes and trajectories for the drive.Publication Gravitational production of scalar dark matter(Springer, 2020-06-12) Ruiz Cembranos, José Alberto; Garay Elizondo, Luis Javier; Sánchez Velázquez, José ManuelWe investigate the gravitational production of scalar dark matter particles during the inflationary and reheating epochs. The oscillatory behavior of the curvature scalarRduring the reheating phase generates two different enhancement mechanisms in the particle production. On the one hand, as it has been already discussed in previous works, it induces tachyonic instabilities in the field which are the dominant enhancement mechanism for light masses. On the other hand, we have found that it also provokes a resonant effect in the ultraviolet region of the spectrum which becomes dominant for masses in the range 10(9)GeV to 10(13)GeV. We have developed an analytical approximation to describe this resonance effect and its consequences on the ultraviolet regime. Once we have calculated the theoretical gravitational production, we constrain the possible values of the phenomenological field parameters to be considered as a dark matter candidate. We do so by comparing the theoretically predicted abundance with the observed one and ensuring that the theoretical prediction does not lead to overproduction. In particular, we find that there is a region of intermediate masses that is forbidden as they would lead to overproduction.Publication Unitary quantization of a scalar charged field and Schwinger effect(Springer, 2020-04-20) Garay Elizondo, Luis Javier; Martín Caro, Alberto García; Martín Benito, MercedesQuantum field theory in curved spacetimes suffers in general from an infinite ambiguity in the choice of Fock representation and associated vacuum. In cosmological backgrounds, the requirement of a unitary implementation of the field dynamics in the physical Hilbert space of the theory is a good criterion to ameliorate such ambiguity. In- deed, this criterion, together with a unitary implementation of the symmetries of the equations of motion, leads to an equivalence class of unitarily equivalent quantizations that, even though it is still formed by an infinite number of Fock representations, is unique. In this work, we apply the procedure developed for fields in cosmological settings to analyze the quantization of a scalar field in the presence of an external electromagnetic classical field in a flat background. We find a natural Fock representation that admits a unitary implementation of the quantum field dynamics. It automatically allows to define a particle number density at all times in the evolution with the correct asymptotic behavior, when the electric field vanishes. Moreover we show the unitary equivalence of all the quantizations that fulfill our criteria, so that they form a unique equivalence class. Although we perform the field quantization in a specific gauge, we also show the equivalence between the procedures taken in different gauges.Publication Quantum unitary dynamics of a charged fermionic field and Schwinger effect(Springer, 2021-10-08) Álvarez Domínguez, Álvaro; Garay Elizondo, Luis Javier; García Heredia, David; Martín Benito, MercedesIn quantum field theory, particle creation occurs, in general, when an intense external field, such as an electromagnetic field, breaks time translational invariance. This leads to an ambiguity in the definition of the vacuum state. In cosmological backgrounds this ambiguity has been reduced by imposing that the quantization preserves the symmetries of the system and that the dynamics is unitarily implemented. In this work, we apply these requirements to the quantization of a massive charged fermionic field coupled to a classical time-dependent homogeneous electric field, extending previous studies done for a scalar field. We characterize the quantizations fulfilling the criteria above and we show that they form a unique equivalence class of unitarily related quantizations, which provide a well-defined number of created particles at all finite times.Publication Causal structure of accelerating black holes(Springer, 2022) Ruiz Cembranos, José Alberto; Garay Elizondo, Luis Javier; Ángel Ortega, SergioAccelerating black holes are described by the so-called C-metric. In this work, we analyse the causal structure of such black holes by using null geodesics. We construct explicitly the relevant Penrose diagrams. First, we recover well-known results associated with the sub-accelerating black holes. Then, we extend the study to the super-accelerating case, in which an additional essential singularity appears. In addition, we consider accelerating black holes with negative masses. We show that they are equivalent to the geometry described by the black hole metric beyond conformal infinity. We compare our results with the Schwarzschild geometry to facilitate understanding and to highlight the interest of the new features.