 Research group
 DF  Nonlinear Fluid Dynamics
 Department
 Department of Applied Physics
 School
 Barcelona School of Architecture (ETSAB)
 ramon.torresherreraupc.edu
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Singularity free gravitational collapse in an effective dynamical quantum spacetime
Torres Herrera, Ramon; Fayos Valles, Francisco
Physics letters B
Date of publication: 20140602
Journal article
Read the abstract Access to the full text Share Reference managersWe model the gravitational collapse of heavy massive shells including its main quantum corrections. Among these corrections, quantum improvements coming from Quantum Einstein Gravity are taken into account, which provides us with an effective quantum spacetime. Likewise, we consider dynamical Hawking radiation by modeling its backreaction once the horizons have been generated. Our results point towards a picture of gravitational collapse in which the collapsing shell reaches a minimum nonzero radius (whose value depends on the shell initial conditions) with its mass only slightly reduced. Then, there is always a rebound after which most (or all) of the mass evaporates in the form of Hawking radiation. Since the mass never concentrates in a single point, no singularity appears. (C) 2014 The Authors. Published by Elsevier B.V.
We model the gravitational collapse of heavy massive shells including its main quantum corrections. Among these corrections, quantum improvements coming from Quantum Einstein Gravity are taken into account, which provides us with an effective quantum spacetime. Likewise, we consider dynamical Hawking radiation by modeling its backreaction once the horizons have been generated. Our results point towards a picture of gravitational collapse in which the collapsing shell reaches a minimum nonzero radius (whose value depends on the shell initial conditions) with its mass only slightly reduced. Then, there is always a rebound after which most (or all) of the mass evaporates in the form of Hawking radiation. Since the mass never concentrates in a single point, no singularity appears.
Postprint (author’s final draft) 
On how energy conservation might prevent black hole explosions and violations of the third law
Torres Herrera, Ramon; Fayos Valles, Francisco
International journal of modern physics D
Date of publication: 20131112
Journal article
Read the abstract Access to the full text Share Reference managersWe claim that imposing energy conservation to the emission of Hawking radiation and to the modelling of black hole evaporation might prevent black hole explosions as well as violations of the third law of black hole thermodynamics. This is specifically shown for the general class of spherically symmetric quantum black holes described by an effective quantum vacuum invariant under boosts in the radial direction. No assumptions are made with regard to the specific framework from which the quantum black holes are derived.
We claim that imposing energy conservation to the emission of Hawking radiation and to the modeling of black hole (BH) evaporation might prevent BH explosions as well as violations of the third law of BH thermodynamics. This is specifically shown for the general class of spherically symmetric quantum BHs described by an effective quantum vacuum invariant under boosts in the radial direction. No assumptions are made with regard to the specific framework from which the quantum BHs are derived.
Preprint of an article published in International journal of modern physics D, 23, 1, 2013, 14500091  145000915 10.1142/S0218271814500096 © copyright World Scientific Publishing Company http://www.worldscientific.com/worldscinet/ijmpd 
On the interior of (quantum) black holes
Torres Herrera, Ramon
Physics letters B
Date of publication: 20130620
Journal article
Read the abstract Access to the full text Share Reference managersDifferent approaches to quantum gravity conclude that black holes may possess an inner horizon, in addition to the (quantum corrected) outer `Schwarzschild¿ horizon. In this Letter we assume the existence of this inner horizon and explain the physical process that might lead to the tunneling of particles through it. It is shown that the tunneling would produce a flux of particles with a spectrum that deviates from the pure thermal one. Under the appropriate approximation the extremely high temperature of this horizon is calculated for an improved quantum black hole. It is argued that the flux of particles tunneled through the horizons affects the dynamics of the black hole interior leading to an endogenous instability.
Different approaches to quantum gravity conclude that black holes may possess an inner horizon, in addition to the (quantum corrected) outer ‘Schwarzschild’ horizon. In this paper we assume the existence of this inner horizon and explain the physical process that might lead to the tunneling of particles through it. It is shown that the tunneling would produce a flux of particles with a spectrum that deviates from the pure thermal one. Under the appropriate approximation the extremely high temperature of this horizon is calculated for an improved quantum black hole. It is argued that the flux of particles tunneled through the horizons affects the dynamics of the black hole interior leading to an endogenous instability.
Published in Physics letters B by ELSEVIER. The original publication is available at http://www.sciencedirect.com/science/article/pii/S0370269313005066 
The mechanism why colliders could create quasistable black holes
Torres Herrera, Ramon; Fayos Valles, Francisco; Lorente Espin, Oscar
International journal of modern physics D
Date of publication: 20130909
Journal article
Read the abstract Access to the full text Share Reference managersIt has been postulated that black holes (BHs) could be created in particle collisions within the range of the available energies for nowadays colliders (LHC). In this paper, we analyze the evaporation of a type of BHs that are candidates for this specific behavior, namely, small BHs on a brane in a world with large extradimensions. We examine their evolution under the assumption that energy conservation is satisfied during the process and compare it with the standard evaporation approach. We claim that, rather than undergoing a quick total evaporation, BHs become quasistable. We comment on the (absence of) implications for safety of this result. We also discuss how the presence of BHs together with the correctness of the energy conservation approach might be experimentally verified.
It has been postulated that black holes could be created in particle collisions within the range of the available energies for nowadays colliders (LHC). In this paper we analyze the evaporation of a type of black holes that are candidates for this specific behaviour, namely, small black holes on a brane in a world with large extradimensions. We examine their evolution under the assumption that energy conservation is satisfied during the process and compare it with the standard evaporation approach. We claim that, rather than undergoing a quick total evaporation, black holes become quasistable. We comment on the (absence of) implications for safety of this result. We also discuss how the presence of black holes together with the correctness of the energy conservation approach might be experimentally verified.
Preprint of an article published in International journal of modern physics D, 22, 13, 2013, 13500861  135008615 10.1142/S0218271813500867 © copyright World Scientific Publishing Company http://www.worldscientific.com/worldscinet/ijmpd 
Evaporation of (quantum) black holes and energy conservation
Torres Herrera, Ramon; Fayos Valles, Francisco; Lorente Espín, Oscar
Physics letters B
Date of publication: 20130128
Journal article
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Cosmological voids and quantum violations of the weak energy conditions
Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20130226
Journal article
Read the abstract View Share Reference managersIn this paper the consequences of quantum gravitational effects in cosmological voids are studied through the use of the wellknown and reliably calculable longrange quantum corrections to the gravitational potential. The lineelement corresponding to these quantummodified voids in a Universe possessing a cosmological constant is obtained. It is shown that the quantum vacuum in the voids is interpretable, through Einstein's equations, as a highly rarefied effective anisotropic fluid permeating the voids. Contrary to the common belief that in our current epoch violations of the energy conditions only take place in relatively small regions of the Universe, it is argued that there may be extremely tiny quantum violations of the weak energy condition in cosmological voids and, therefore, in enormous regions occupying most of the volume of the Universe. 
Mechanism of quasistabilization of primordial black holes
Torres Herrera, Ramon
Physical review. D, Particles, fields, gravitation, and cosmology
Date of publication: 20130617
Journal article
Read the abstract Access to the full text Share Reference managersIt is argued that primordial black holes with initial masses satisfying M<1015¿¿g, instead of having explode, might currently be in a quasistable phase contributing to a tiny fraction of the measured dark matter. This statement is based on a computation of black hole evaporation in which energy conservation is taken into account that shows that the backreaction to Hawking radiation favors the quasistabilization of the black hole. The result is specifically shown for general spherically symmetric quantum black holes described by an effective metric independently of the specific framework from which it is derived. The quintessential primordial black hole is fully analyzed as an example.
It is argued that primordial black holes with initial masses satisfying M<1015 g, instead of having explode, might currently be in a quasistable phase contributing to a tiny fraction of the measured dark matter. This statement is based on a computation of black hole evaporation in which energy conservation is taken into account that shows that the backreaction to Hawking radiation favors the quasistabilization of the black hole. The result is specifically shown for general spherically symmetric quantum black holes described by an effective metric independently of the specific framework from which it is derived. The quintessential primordial black hole is fully analyzed as an example. 
On the effect of energy conservation on black hole evaporation
Torres Herrera, Ramon; Fayos Valles, Francisco; Lorente Espín, Oscar
International journal of modern physics D
Date of publication: 20130423
Journal article
Read the abstract View Share Reference managersWe consider the emission of Hawking radiation by black holes as a consequence of a tunneling process. By requiring energy conservation in the derivation of the emission rate we get a wellknown deviation from an exact thermal spectrum. A model that takes into account the implications of energy conservation, as well as the backscattered radiation, is then constructed in order to describe the evolution of black holes as they evaporate. The evaporation process in this model is compared with the results in the standard "thermal" approximation. This allows us to point out the relevance that energy conservation might have in the last stages of black hole evaporation. We also comment about the possible implications of energy conservation in the information loss paradox. 
On the invariant causal characterization of singularities in spherically symmetric spacetimes
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20120418
Journal article
Read the abstract Access to the full text Share Reference managersThe causal character of singularities is often studied in relation to the existence of naked singularities and the subsequent possible violation of the cosmic censorship conjecture. Generally, one constructs a model in the framework of general relativity described in some specific coordinates and finds an ad hoc procedure to analyze the character of the singularity. In this paper, we show that the causal character of the zeroarealradius (R = 0) singularity in spherically symmetric models is related to some specific invariants. In this way, if some assumptions are satisfied, one can ascertain the causal character of the singularity algorithmically through the computation of these invariants and, therefore, independent of the coordinates used in the model. 
Invariant identification of naked singularities in spherically symmetric spacetimes
Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20120910
Journal article
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Física Aplicada a la arquitectura: calor, psicrometría y transferencia de calor
Torres Herrera, Ramon
Date of publication: 20120830
Book
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An approach to evaporating stars and black holes
Fayos Valles, Francisco; Torres Herrera, Ramon
Journal of physics: conference series
Date of publication: 20110901
Journal article
Read the abstract Access to the full text Share Reference managersMany models in which the object under study loses all its mass have appeared in the literature. No doubt, the most eminent examples are the models for evaporating black holes and for evaporating stars. Here we describe a semiclassical study of these evaporating models centered on the evaporating event itself. We pay special attention to the evaporating models as a means of avoiding singularities during the collapse. In case of any preexisting nonspacelike curvature singularity, we show that these models tend to evaporate it.
Many models in which the object under study loses all its mass have appeared in the literature. No doubt, the most eminent examples are the models for evaporating black holes and for evaporating stars. Here we describe a semiclassical study of these evaporating models centered on the evaporating event itself. We pay special attention to the evaporating models as a means of avoiding singularities during the collapse. In case of any preexisting nonspacelike curvature singularity, we show that these models tend to evaporate it. 
On the causal characterization of singularities in spherically symmetric spacetimes
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20111014
Journal article
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A quantum improvement to the gravitational collapse of radiating stars
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20110406
Journal article
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Local behaviour of evaporating stars and black holes around the total evaporation event
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20100621
Journal article
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An approach to evaporating stars and black holes
Fayos Valles, Francisco; Torres Herrera, Ramon
Spanish Relativity Meeting
Presentation's date: 2010
Presentation of work at congresses
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A class of interiors for Vaidya's radiating metric: singularityfree gravitational collapse
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 20080901
Journal article
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Some aspects of bubbles and voids in a cosmological context
Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 2005
Journal article
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Spherically symmetric models for stars and voids II: Constrains on the radial pressures
Fayos Valles, Francisco; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 200402
Journal article
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Spherically symmetric models for charged stars and voids: I. Charge bound
Fayos Valles, Francisco; Senovilla, José M M; Torres Herrera, Ramon
Classical and quantum gravity
Date of publication: 200305
Journal article
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CONSTRUCCION DE MODELOS DE ESTRELLAS Y BURBUJAS DE VACIO O RADIATIVAS, EN EL MARCO DE LA RELATIVIDAD GENERAL : UN PLANTEAMIENTO GLOBAL
Torres Herrera, Ramon
Defense's date: 20011015
Department of Applied Physics, Universitat Politècnica de Catalunya
Theses
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Constructing models for stars and voids in the universe: a Comprehensive approach
Fayos Valles, Francisco; Torres Herrera, Ramon
XXIII Spanish Relativity Meeting
Presentation of work at congresses
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Some reflections on the spherically matching
Fayos Valles, Francisco; Senovilla, J M M; Torres Herrera, Ramon
Encuentros Relativistas Españoles 96: Some Topics on General Relativity and Gravitational Radiation
Presentation of work at congresses
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Some reflections on the spherically symmetric matching
Fayos Valles, Francisco; Senovilla, J M M; Torres Herrera, Ramon
Spanish relativity meeting '96
Presentation of work at congresses
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General matching of two spherically symmetric spacetimes
Fayos Valles, Francisco; Senovilla, J M M; Torres Herrera, Ramon
Physical review. D, Particles, fields, gravitation, and cosmology
Date of publication: 19961001
Journal article
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