Hawking radiation in large N strongly-coupled field theories

TL;DR

This paper investigates the behavior of strongly coupled large N field theories on black hole backgrounds using AdS/CFT, revealing two distinct phases characterized by either connected or disconnected horizons and their thermal exchange properties.

Contribution

It introduces the concept of black funnels and discusses the phase transition between connected and disconnected horizon configurations in the dual gravitational description.

Findings

Black funnels represent a phase with strong coupling to plasma.

Small black holes exhibit weak coupling, resembling confined phases.

A sharp transition separates the two behaviors at large N and strong coupling.

Abstract

We consider strongly coupled field theories at large N on black hole backgrounds. At sufficiently high Hawking temperature T_H, one expects a phase where the black hole is in equilibrium with a deconfined plasma. We explore this phase in the context of the AdS/CFT correspondence, and argue that two possible behaviors may result. At a given Hawking temperature T_H, field theories on large black hole backgrounds will couple strongly to the plasma and will be dual to novel bulk spacetimes having a single connected horizon which we dub {\it black funnels}. We construct examples of black funnels in low spacetime dimensions for different classes of field theory black holes. In this case, perturbing the equilibrium state results in the field theory exchanging heat with the black hole at a rate typical of conduction through deconfined plasma. In contrast, we argue that due to the finite physical size of plasma excitations, smaller black holes will couple only weakly to the field theory excitations. This situation is dual to bulk solutions containing two disconnected horizons which remain to be constructed. Here perturbations lead to heat exchange at a level typical of confined phases, even when T_H remains far above any deconfinement transition. At least at large N and strong coupling, these two behaviors are separated by a sharp transition. Our results also suggest a richer class of brane-world black holes than hitherto anticipated.