A worldsheet for Kerr

TL;DR

This paper interprets the Newman-Janis shift property of Kerr solutions as a worldsheet effective action, extending its applicability to gravity and electrodynamics, and explores its implications for leading interactions using spinor-helicity methods.

Contribution

It introduces a worldsheet perspective on the Newman-Janis shift, connecting classical solutions with effective actions and scattering amplitude techniques.

Findings

Newman-Janis shift can be viewed as a worldsheet effective action.

The shift property applies to leading interactions of Kerr black holes.

Chiral equations of motion and spinor-helicity methods facilitate this analysis.

Abstract

We show that the Newman-Janis shift property of the exact Kerr solution can be interpreted in terms of a worldsheet effective action. This holds both in gravity, and for the single-copy $\sqrt{\text{Kerr}}$ solution in electrodynamics. At the level of equations of motion, we show that the Newman-Janis shift holds also for the leading interactions of the Kerr black hole. These leading interactions are conveniently described using chiral classical equations of motion with the help of the spinor-helicity method familiar from scattering amplitudes.