2,749 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
Vacuum decay in an interacting multiverse
We examine a new multiverse scenario in which the component universes
interact. We focus our attention to the process of "true" vacuum nucleation in
the false vacuum within one single element of the multiverse. It is shown that
the interactions lead to a collective behaviour that might lead, under specific
conditions, to a pre-inflationary phase and ensued distinguishable imprints in
the comic microwave background radiation.Comment: 9 pages, 5 figure
Conceptual Challenges on the Road to the Multiverse
The current debate about a possible change of paradigm from a single universe to a multiverse scenario could have deep implications on our view of cosmology and of science in general. These implications therefore deserve to be analyzed from a fundamental conceptual level. We briefly review the different multiverse ideas, both historically and within contemporary physics. We then discuss several positions within philosophy of science with regard to scientific progress, and apply these to the multiverse debate. Finally, we construct some key concepts for a physical multiverse scenario and discuss the challenges this scenario has to deal with in order to provide a solid, testable theory
Quantum Gravity Phenomenology from the Thermodynamics of Spacetime
This work is based on the formalism developed in the study of the thermodynamics of spacetime used to derive Einstein equations from the proportionality of entropy within an area. When low-energy quantum gravity effects are considered, an extra logarithmic term in the area is added to the entropy expression. Here, we present the derivation of the quantum modified gravitational dynamics from this modified entropy expression and discuss its main features. Furthermore, we outline the application of the modified dynamics to cosmology, suggesting the replacement of the Big Bang singularity with a regular bounce
Thermodynamics of spacetime from minimal area
Motivated by exploring the interface between thermodynamics of spacetime and quantum gravity effects, we develop a heuristic derivation of Hawking temperature and Bekenstein entropy from the existence of a minimal resolvable area. Moreover, we find leading order quantum gravity corrections to them that are in qualitative agreement with results obtained by other methods, both heuristic and rigorous. In this way, we recover, as a particular case, the corrections heuristically obtained from the existence of minimal length. We also show that the size of minimal area is constrained from above by well understood results of semiclassical black hole physics, specifically by the entropy content of Hawking radiation. The minimal area derivation we introduce is also applied to finding the Unruh temperature associated with causal diamonds and to establish a new relation between this temperature and the entropy of the causal diamond's horizon
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