Dynamical black holes and expanding plasmas

TL;DR

This paper investigates the structure of dynamic black hole geometries dual to expanding plasmas, comparing approximate and exact solutions, and explores how horizon areas relate to entropy in the dual field theory.

Contribution

It provides a detailed analysis of event and apparent horizons in two dual geometries, highlighting the significance of the apparent horizon for entropy interpretation.

Findings

The apparent horizon area remains finite and constant in the conformal soliton flow.

The event horizon area diverges in the conformal soliton geometry.

The geometry dual to Bjorken flow is constructed perturbatively at late times.

Abstract

We analyse the global structure of time-dependent geometries dual to expanding plasmas, considering two examples: the boost invariant Bjorken flow, and the conformal soliton flow. While the geometry dual to the Bjorken flow is constructed in a perturbation expansion at late proper time, the conformal soliton flow has an exact dual (which corresponds to a Poincare patch of Schwarzschild-AdS). In particular, we discuss the position and area of event and apparent horizons in the two geometries. The conformal soliton geometry offers a sharp distinction between event and apparent horizon; whereas the area of the event horizon diverges, that of the apparent horizon stays finite and constant. This suggests that the entropy of the corresponding CFT state is related to the apparent horizon rather than the event horizon.