arXiv subjects

Abram Akal

Publications and source records attributed to Abram Akal.

5 recordsLinked to original sources

arXiv2026

On the temperature of the quantum black hole

A nontrivial peculiarity of general relativity is that when the horizon region of black holes is rendered harmless, the exterior doubles, resulting in a causally disconnected parallel universe. This intricacy plays a central role in 't Hooft's unitarity arguments, emphasising an exact identification between the physical universe and its duplicate on the other side of the horizon. However, it leads to another tension in the form of a factor of two correction in Hawking's temperature. This discrepancy is concerning because the Rindler temperature is universal and complies with the Bekenstein-Hawking entropy. We demonstrate that the mismatch in the Boltzmann factor gets fixed if the state that forms the corresponding density matrix adopts a generalised thermofield double structure. That leaves room for some interesting discussion.

hep-th↗

arXiv2024

Information storage and near horizon quantum correlations

It is usually stated that the information storing region associated with the Bekenstein-Hawking entropy is enclosed by a sphere of diameter equal twice the Schwarzschild radius. We point out that this cannot apply to a quantum black hole. The deviation is particularly revealed when the latter is maximally correlated with its Hawking radiation. Specifically, we demonstrate that the size of the entropy sphere associated with the underlying microstructure has to be necessarily broadened when the fine grained radiation entropy becomes maximal. Such an enlargement is understood to be the consequence of unitarization effects in quantum gravity and aligns with recent findings in holography arguing that purification happens via semiclassically invisible quantum correlations extending across the black hole atmosphere. In the present work, we consider an evaporating black hole in asymptotically flat spacetime. We assume that the standard thermodynamical description is valid so long the black hole viewed from the outside is sufficiently large, radiation escaping into the future null infinity can be described on a smooth spacetime background, and the von Neumann entropy of Hawking radiation evolves unitarily. We briefly comment on the black hole singularity.

hep-th↗

arXiv2024

Universality, intertwiners and black hole information

The central question in this article is how information does leak out from black holes. Relying on algebraic arguments and the concept of superselection sectors, we propose the existence of certain operators whose correlations extend across the black hole atmosphere and range into the interior. Contained in the full algebra, these black hole intertwiners will not belong to the subalgebra describing semiclassical bulk physics. We study this proposal in the context of operator reconstructions for code spaces containing a large number of microstates. As long as the atmosphere is excluded from a particular subsystem, the global state seen under the action of the associated algebra is maximally mixed and therefore described by a single classical background. Once the relevant correlations are encoded, i.e. if the algebra is sufficiently enlarged, perfect state distinguishability becomes possible. We arrive at this by computing the von Neumann entropy which may explain the result obtained by applying the quantum extremal surface prescription to the mixed state. We then examine these insights in the context of black hole evaporation and argue that information is transferred to the radiation via black hole intertwiners. We derive the Page curve. The mechanism above suggests that black hole information is topologically protected. An infalling observer would experience no drama. This may resolve the unitarity problem without running into any firewall or state puzzle, the latter being evident in generalized entropy computations. We also examine the question of how certain wormhole topologies may be understood given these findings. We argue that their occurrence in gravity replica computations may be related to the maximal correlation between radiation and atmosphere surrounding the old black hole. This may suggest a connection between topology change and near horizon quantum gravitational effects.

hep-th↗

arXiv2024

Breakdown of quantum mechanics in gravitational holography

According to the holographic principle, the information content assigned to a gravitational region is processed by its lower dimensional boundary. As an example setup compatible with this principle, the AdS/CFT correspondence relies on the existence of D-branes in superstring theory. Black hole complementarity is inevitably linked to holography and states that information associated with the collapsed pure state is reflected in the near horizon region. Yet, if this is so, it is indispensable to understand the mechanism that makes black holes viewed from the outside evolve unitarily. We here argue that the information preserving quantum atmosphere of the black hole emerges from hidden variables on its horizon which would necessitate going beyond a probabilistic description within standard quantum theory. In AdS/CFT, this would mean that the completion of the semiclassical subalgebra to the complete boundary algebra has to be traced back to the emergent near horizon Hilbert space structure. The present investigations suggest that spacetime horizons, in general, may play a crucial role in restoring a long speculated ontology in quantum mechanics.

hep-th↗

arXiv2022

Exact instantons via worldline deformations

The imaginary part of the one loop effective action in external backgrounds can be efficiently computed using worldline instantons which are closed periodic paths in spacetime. Exact solutions for nonstatic backgrounds are only known in certain cases. In this paper, we propose a novel technique allowing the construction of further exactly solvable models. In order to do so, we introduce a deformation function which maps the worldline instantons for a given model to the closed periodic stationary paths of a new model. Executing this procedure iteratively results in a chain of infinitely many solvable models. Similar ideas were applied to topological and nontopological defects in quantum field theory. We explicitly discuss the tunneling exponential in the Schwinger pair creation rate and illustrate the validity of the proposed technique for well-known cases.

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