Superrotations and Black Hole Pair Creation

TL;DR

This paper demonstrates that finite superrotations in asymptotically flat spacetimes can be physically interpreted as transformations connecting spacetimes with cosmic string defects, especially in the context of black hole pair creation and decay.

Contribution

It provides a physical interpretation of superrotations by linking them to spacetimes with cosmic string defects in black hole pair creation scenarios.

Findings

Finite superrotations relate initial and final spacetimes with cosmic string defects.

Black hole pair creation via the $C$-metric involves superrotation transformations.

Spacetimes with cosmic strings exhibit asymptotic symmetries including superrotations.

Abstract

Recent work has shown that the symmetries of classical gravitational scattering in asymptotically flat spacetimes include, at the linearized level, infinitesimal superrotations. These act like Virasoro generators on the celestial sphere at null infinity. However, due to the singularities in these generators, the physical status of finite superrotations has remained unclear. Here we address this issue in the context of the breaking of a cosmic string via quantum black hole pair nucleation. This process is described by a gravitational instanton known as the $C$-metric. After pair production, the black holes are pulled by the string to null infinity with a constant acceleration. At late times the string decays and the spacetime settles into a vacuum state. We show that the early and late spacetimes before and after string decay differ by a finite superrotation. This provides a physical interpretation of superrotations. They act on spacetimes which are asymptotically flat everywhere except at isolated singularities with cosmic string defects.