Black Hole Microstate Cosmology

TL;DR

This paper investigates the holographic duals of black hole microstates with a geometrical behind-the-horizon region, analyzing entanglement entropy dynamics and proposing a connection to cosmological models via ETW branes.

Contribution

It introduces a model linking black hole microstates to cosmological scenarios using ETW branes and studies entanglement entropy to probe behind-the-horizon physics.

Findings

Entanglement entropy reveals behind-the-horizon physics.

Qualitative agreement with SYK model calculations.

Potential gravity localization on ETW branes leading to cosmological models.

Abstract

In this note, we explore the possibility that certain high-energy holographic CFT states correspond to black hole microstates with a geometrical behind-the-horizon region, modelled by a portion of a second asymptotic region terminating at an end-of-the-world (ETW) brane. We study the time-dependent physics of this behind-the-horizon region, whose ETW boundary geometry takes the form of a closed FRW spacetime. We show that in many cases, this behind-the-horizon physics can be probed directly by looking at the time dependence of entanglement entropy for sufficiently large spatial CFT subsystems. We study in particular states defined via Euclidean evolution from conformal boundary states and give specific predictions for the behavior of the entanglement entropy in this case. We perform analogous calculations for the SYK model and find qualitative agreement with our expectations. A fascinating possibility is that for certain states, we might have gravity localized to the ETW brane as in the Randall-Sundrum II scenario for cosmology. In this case, the effective description of physics beyond the horizon could be a big bang/big crunch cosmology of the same dimensionality as the CFT. In this case, the d-dimensional CFT describing the black hole microstate would give a precise, microscopic description of the d-dimensional cosmological physics.