Horizons and plane waves: A review

TL;DR

This review discusses the challenges and methods of constructing black hole and black string solutions in asymptotically plane wave spacetimes, highlighting the limitations imposed by symmetries and presenting new solution-generating techniques.

Contribution

The paper introduces two solution-generating methods to construct asymptotically plane wave black string/brane geometries, overcoming previous symmetry restrictions.

Findings

pp-waves cannot describe black holes due to symmetry constraints

Relaxing symmetry allows for regular event horizons in plane wave spacetimes

New solution techniques enable construction of asymptotically plane wave black objects

Abstract

We review the attempts to construct black hole/string solutions in asymptotically plane wave spacetimes. First, we demonstrate that geometries admitting a covariantly constant null Killing vector cannot admit event horizons, which implies that pp-waves can't describe black holes. However, relaxing the symmetry requirements allows us to generate solutions which do possess regular event horizons while retaining the requisite asymptotic properties. In particular, we present two solution generating techniques and use them to construct asymptotically plane wave black string/brane geometries.