Person: Garay Elizondo, Luis Javier
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 11
PublicationQuantum behavior of FRW radiation-filled universes(Amer Physical Soc, 2002-09-15) Bouhmadi Lopez, M.; Garay Elizondo, Luis Javier; González Díaz, Pedro F.We study the quantum vacuum fluctuations around closed Friedmann-Robertson-Walker (FRW) radiation-filled universes with a nonvanishing cosmological constant. These vacuum fluctuations are represented by a conformally coupled massive scalar field and are treated in the lowest order of perturbation theory. In the semiclassical approximation, the perturbations are governed by differential equations which, properly linearized, become generalized Lame equations. The wave function thus obtained must satisfy appropriate regularity conditions which ensure its finiteness for every field configuration. We apply these results to asymptotically anti-de Sitter Euclidean wormhole spacetimes and show that there is no catastrophic particle creation in the Euclidean region, which would lead to divergences of the wave function. PublicationSonic analog of gravitational black holes in Bose-Einstein condensates(American Physical Society, 2000-11-27) Garay Elizondo, Luis Javier; Anglin, J. R.; Cirac, J. I.; Zoller, P.It is shown that, in dilute-gas Bose-Einstein condensates, there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit a behavior resembling that of gravitational black holes. The dynamical instabilities involve creation of quasiparticle pairs in positive and negative energy states, as in the well-known suggested mechanism for black-hole evaporation. We propose a scheme to generate a stable sonic black hole in a ring trap. PublicationImmirzi ambiguity in the kinematics of quantum general relativity(Amer Physical Soc, 2002-07-15) Garay Elizondo, Luis Javier; Mena Marugán, Guillermo A.The Immirzi ambiguity arises in loop quantum gravity when geometric operators are represented in terms of different connections that are related by means of an extended Wick transform. We analyze the action of this transform in gravity coupled with matter fields and discuss its analogy with the Wick rotation on which the Thiemann transform between Euclidean and Lorentzian gravity is based. In addition, we prove that the effect of this extended Wick transform is equivalent to a constant scale transformation as far as the symplectic structure and kinematical constraints are concerned. This equivalence is broken in the dynamical evolution. Our results are applied to the discussion of the black hole entropy in the limit of large horizon areas. We first argue that, since the entropy calculation is performed for horizons of fixed constant area, one might in principle choose an Immirzi parameter that depends on this quantity. This would spoil the linearity with the area in the entropy formula. We then show that the Immirzi parameter appears as a constant scaling in all the steps where dynamical information plays a relevant role in the entropy calculation. This fact, together with the kinematical equivalence of the Immirzi ambiguity with a change of scale, is used to preclude the potential nonlinearity of the entropy on physical grounds. PublicationHybrid quantum Gowdy cosmology: combining loop and Fock quantizations(Amer Physical Soc, 2008-10) Martin Benito, M.; Garay Elizondo, Luis Javier; Mena Marugán, Guillermo A.We quantize an inhomogeneous cosmological model using techniques that include polymeric quantization. More explicitly, we construct well-defined operators to represent the constraints and find the physical Hilbert space formed by their solutions, which reproduces the conventional Fock quantization for the inhomogeneities. The initial singularity is resolved in this inhomogeneous model in an extremely simple way and without imposing special boundary conditions, thus ensuring the robustness and generality of this resolution. Furthermore, this quantization constitutes a well-founded step towards the extraction of physical results and consequences from loop quantum cosmology, given the central role of the inhomogeneities in modern cosmology. PublicationSonic black holes in dilute Bose-Einstein condensates(American Physical Society, 2001-02) Garay Elizondo, Luis Javier; Cirac, J. I.; Anglin, J. R.; Zoller, P.The sonic analog of a gravitational black hole in dilute-gas Bose-Einstein condensates is investigated. It is shown that there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit behaviors completely analogous to that of gravitational black holes. The dynamical instabilities involve the creation of quasiparticle pairs in positive and negative energy states. We illustrate these features in two qualitatively different one-dimensional models, namely, a long, thin condensate with an outcoupler laser beam providing an "atom sink" and a tight ring-shaped condensate. We also simulate the creation of a stable sonic black hole by solving the Gross-Pitaevskii equation numerically for a condensate subject to a trapping potential which is adiabatically deformed. A sonic black hole could, in this way, be created experimentally with state-of-the-art or planned technology. PublicationReal clocks and the Zeno effect(American Physical Society, 2003-08) Egusquiza, Iñigo L.; Garay Elizondo, Luis JavierReal clocks are not perfect. This must have an effect in our predictions for the behavior of a quantum system, an effect for which we present a unified description, encompassing several previous proposals. We study the relevance of clock errors in the Zeno effect and find that generically no Zeno effect can be present (in such a way that there is no contradiction with currently available experimental data). We further observe that, within the class of stochasticities in time addressed here, there is no modification in emission line shapes. PublicationStability analysis of sonic horizons in Bose-Einstein condensates(Amer Physical Soc, 2006-07) Barceló, C.; Cano, A.; Garay Elizondo, Luis Javier; Jannes, G.We examine the linear stability of various configurations in Bose-Einstein condensates with steplike sonic horizons. These configurations are chosen in analogy with gravitational systems with a black hole horizon, a white hole horizon, and a combination of both. We discuss the role of different boundary conditions in this stability analysis, paying special attention to their meaning in gravitational terms. We highlight that the stability of a given configuration, not only depends on its specific geometry, but especially on these boundary conditions. Under boundary conditions directly extrapolated from those in standard general relativity, black hole configurations, white hole configurations, and the combination of both into a black hole-white hole configuration are shown to be stable. However, we show that under other (less stringent) boundary conditions, configurations with a single black hole horizon remain stable, whereas white hole and black hole-white hole configurations develop instabilities associated to the presence of the sonic horizons. PublicationQuantum time uncertainty in Schwarzschild-anti-de Sitter black holes(Amer Physical Soc, 2007-08) Galan, Pablo; Garay Elizondo, Luis Javier; Mena Marugán, Guillermo A.The combined action of gravity and quantum mechanics gives rise to a minimum time uncertainty in the lowest order approximation of a perturbative scheme, in which quantum effects are regarded as corrections to the classical spacetime geometry. From the nonperturbative point of view, both gravity and quantum mechanics are treated on equal footing in a description that already contains all possible backreaction effects as those above in a nonlinear manner. In this paper, the existence or not of such minimum time uncertainty is analyzed in the context of Schwarzschild-anti-de Sitter black holes using the isolated horizon formalism. We show that from a perturbative point of view, a nonzero time uncertainty is generically present owing to the energy scale introduced by the cosmological constant, while in a quantization scheme that includes nonperturbatively the effects of that scale, an arbitrarily high time resolution can be reached. PublicationImmirzi ambiguity, boosts and conformal frames for black holes(IOP Publishing Ltd, 2003-04-21) Garay Elizondo, Luis Javier; Mena Marugán, Guillermo A.We analyse changes of the Immirzi parameter in loop quantum gravity and compare their consequences with those of Lorentz boosts and constant conformal transformations in black-hole physics. We show that the effective value deduced for the Planck length in local measurements of vacuum black holes by an asymptotic observer may depend on its conformal or Lorentz frame. This introduces an apparent ambiguity in the expression of the black-hole entropy which is analogous to that produced by the Immirzi parameter. For quantities involving a notion of energy, the similarity between the implications of the Immirzi ambiguity and a conformal scaling disappears, but the parallelism with boosts is maintained. PublicationSensitivity of Hawking radiation to superluminal dispersion relations(Amer Physical Soc, 2009-01) Barceló, C.; Garay Elizondo, Luis Javier; Jannes, G.We analyze the Hawking radiation process due to collapsing configurations in the presence of superluminal modifications of the dispersion relation. With such superluminal dispersion relations, the horizon effectively becomes a frequency-dependent concept. In particular, at every moment of the collapse, there is a critical frequency above which no horizon is experienced. We show that, as a consequence, the late-time radiation suffers strong modifications, both quantitative and qualitative, compared to the standard Hawking picture. Concretely, we show that the radiation spectrum becomes dependent on the measuring time, on the surface gravities associated with different frequencies, and on the critical frequency. Even if the critical frequency is well above the Planck scale, important modifications still show up.