312 research outputs found
Multi-partite analysis of average-subsystem entropies
So-called average subsystem entropies are defined by first taking partial
traces over some pure state to define density matrices, then calculating the
subsystem entropies, and finally averaging over the pure states to define the
average subsystem entropies. These quantities are standard tools in quantum
information theory, most typically applied in bipartite systems. We shall first
present some extensions to the usual bipartite analysis, (including a
calculation of the average tangle, and a bound on the average concurrence),
follow this with some useful results for tripartite systems, and finally extend
the discussion to arbitrary multi-partite systems. A particularly nice feature
of tri-partite and multi-partite analyses is that this framework allows one to
introduce an "environment" for small subsystems to couple to.Comment: Minor changes. 1 reference added. Published versio
Entropy budget for Hawking evaporation
Blackbody radiation, emitted from a furnace and described by a Planck
spectrum, contains (on average) an entropy of bits per photon.
Since normal physical burning is a unitary process, this amount of entropy is
compensated by the same amount of "hidden information" in correlations between
the photons. The importance of this result lies in the posterior extension of
this argument to the Hawking radiation from black holes, demonstrating that the
assumption of unitarity leads to a perfectly reasonable entropy/information
budget for the evaporation process. In order to carry out this calculation we
adopt a variant of the "average subsystem" approach, but consider a tripartite
pure system that includes the influence of the rest of the universe, and which
allows "young" black holes to still have a non-zero entropy; which we identify
with the standard Bekenstein entropy.Comment: Proceedings of the conference "VARCOSMOFUN'16" in Szczecin, Poland,
12-17 September, 2016. Accepted for publication in "Universe", belonging to
the Special Issue "Varying Constants and Fundamental Cosmology
Generalized uncertainty principle impact onto the black holes information flux and the sparsity of Hawking radiation
We investigate the generalized uncertainty principle (GUP) corrections to the
entropy content and the information flux of black holes, as well as the
corrections to the sparsity of the Hawking radiation at the late stages of
evaporation. We find that due to these quantum gravity motivated corrections,
the entropy flow per particle reduces its value on the approach to the Planck
scale due to a better accuracy in counting the number of microstates. We also
show that the radiation flow is no longer sparse when the mass of a black hole
approaches Planck mass which is not the case for non-GUP calculations.Comment: 6 pages, 2 figures, typos corrected, published in Phys. Rev.
Minimal length and the flow of entropy from black holes
The existence of a minimal length, predicted by different theories of quantum
gravity, can be phenomenologically described in terms of a generalized
uncertainty principle. We consider the impact of this quantum gravity motivated
effect onto the information budget of a black hole and the sparsity of Hawking
radiation during the black hole evaporation process. We show that the
information is not transmitted at the same rate during the final stages of the
evaporation and that the Hawking radiation is not sparse anymore when the black
hole approaches the Planck mass.Comment: Awarded Honorable Mention in the 2018 Gravity Research Foundation
Essay Competitio
quantum cosmology: avoiding the Big Rip
Extended theories of gravity have gathered a lot of attention over the last
years, for they not only provide an excellent framework to describe the
inflationary era but also yields an alternative to the elusive and mysterious
dark energy. Among the different extended theories of gravity, on this work we
focus on metric theories. In addition, it is well known that if the
late-time acceleration of the universe is stronger than the one induced by a
cosmological constant then some future cosmic singularities might arise, being
the Big Rip the most virulent one. Following this reasoning, on this work, we
analyse the Big Rip singularity in the framework of quantum
geometrodynamics. Invoking the DeWitt criterium, i. e. that the wave function
vanishes at the classical singularity, we proof that a class of solutions to
the Wheeler-DeWitt equation fulfilling this condition can be found. Therefore,
this result hints towards the avoidance of the Big Rip in metric
theories of gravity.Comment: V1:13 pages. Dedicated to the memory of Prof. Pedro F. Gonzalez-Diaz
(our former PhD supervisor). V2: 9 pages (new style), minor clarifications
included, no physics changes, 6 references added. Version accepted for
publication in Physical Review
New perspective on thermodynamics of spacetime: The emergence of unimodular gravity and the equivalence of entropies
We present a novel derivation of Einstein equations from the balance between
Clausius entropy crossing the boundary of a local causal diamond and
entanglement entropy associated with its horizon. Comparing this derivation
with the entanglement equilibrium approach developed by Jacobson, we are able
to argue for the equivalence of matter entanglement and Clausius entropy in the
semiclassical regime. We also provide a direct comparison of both entropies for
conformal matter, showing their equivalence without appealing to gravitational
dynamics. Furthermore, we determine that gravitational dynamics implied by
thermodynamics of spacetime, in fact, corresponds to unimodular gravity rather
than general relativity.Comment: 19 pages, 1 figure Version accepted in PRD. Few typos corrected and
some references adde
Thermodynamics of spacetime and unimodular gravity
In this review we discuss emergence of unimodular gravity (or, more
precisely, Weyl transverse gravity) from thermodynamics of spacetime. By
analyzing three different ways to obtain gravitational equations of motion by
thermodynamic arguments, we show that the results point to unimodular rather
than fully diffeomorphism invariant theories and that this is true even for
modified gravity. The unimodular character of dynamics is especially evident
from the status of cosmological constant and energy-momentum conservation.Comment: 16 pages, 2 figures. Review prepared for a Special Issue of the
International Journal of Geometric Methods in Modern Physics dedicated to the
conference Geometric Foundations of Gravity 202
Emergence of quadratic gravity from entanglement equilibrium
In this work, we derive the linearised equations of quadratic gravity from
entanglement equilibrium of local causal diamonds. Rather than starting from
the Wald entropy prescription (which depends on the gravitational Lagrangian),
we employ a model independent approach based on the logarithmic corrections to
horizon entanglement entropy. In this way, we are able to show the emergence of
linearised quadratic gravity from entanglement equilibrium without using any a
priori knowledge about gravitational dynamics. If the logarithmic correction to
entropy has a negative sign, as predicted by replica trick calculations of
entanglement entropy, we find that the quadratic gravity correction terms have
the sign necessary to avoid tachyonic instabilities of the theory.Comment: 8 pages, 1 figure. Matches the version accepted in PR
Quantum phenomenological gravitational dynamics: A general view from thermodynamics of spacetime
In this work we derive general quantum phenomenological equations of
gravitational dynamics and analyse its features. The derivation uses the
formalism developed in thermodynamics of spacetime and introduces low energy
quantum gravity modifications to it. Quantum gravity effects are considered via
modification of Bekenstein entropy by an extra logarithmic term in the area.
This modification is predicted by several approaches to quantum gravity,
including loop quantum gravity, string theory, AdS/CFT correspondence and
generalised uncertainty principle phenomenology, giving our result a general
character. The derived equations generalise classical equations of motion of
unimodular gravity, instead of the ones of general relativity, and they contain
at most second derivatives of the metric. We provide two independent
derivations of the equations based on thermodynamics of local causal diamonds.
First one uses Jacobson's maximal vacuum entanglement hypothesis, the second
one Clausius entropy flux. Furthermore, we consider questions of diffeomorphism
and local Lorentz invariance of the resulting dynamics and discuss its
application to a simple cosmological model, finding a resolution of the
classical singularity.Comment: Extended discussions, extra references added. 31 pages, 1 figur
Road to the multiverse paved by quantum interactions
Presentación de 20 diapositivas; JARRAMPLAS’15; La Casería (Navaconcejo, Valle del Jerte), Cáceres, España, 24–27 Marzo 2015)Peer Reviewe
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