Radiation in Fluid/Gravity and the Flat Limit

TL;DR

This paper investigates the relationship between bulk gravitational radiation and boundary fluid dynamics in asymptotically AdS spacetimes, exploring the flat limit and flat-space holography with explicit examples.

Contribution

It introduces a holographic framework connecting bulk radiation to boundary fluid variables and extends this to flat-space holography with Carrollian structures.

Findings

Bulk radiation correlates with dissipative boundary stress tensor corrections.

Bulk radiation sources Carrollian viscous stress tensor and heat current.

Explicit examples include Robinson-Trautman spacetimes and accelerating black holes.

Abstract

We explore asymptotically locally anti-de Sitter spacetimes exhibiting gravitational radiative behavior, employing null gauges that allow for a well-defined flat limit. The radiative content in the bulk is captured by the boundary Cotton and stress tensor, which we collect into a radiative vector. We reinterpret this vector holographically in terms of fluid variables in the dual boundary theory. For algebraically special solutions, we uncover a close connection between bulk radiation and dissipative corrections in the boundary stress tensor, demonstrating a direct link between radiation and entropy production in the boundary fluid. This reveals a rich interplay between radiative dynamics in the bulk and out-of-equilibrium conformal physics at the boundary. We then investigate the flat limit of this correspondence in the context of flat-space holography. In this setting, we construct a Carrollian analogue of the radiative vector and introduce Celestial observables, such as energy detectors, which emerge naturally from the bulk's radiative structure. Our analysis shows that bulk radiation sources the Carrollian viscous stress tensor and heat current, which encodes the Bondi news in this framework. We illustrate our results with explicit examples, including Robinson-Trautman spacetimes and accelerating black holes.