Abstract

Gauge-gravity duality is arguably our best hope for understanding quantum gravity. Considerable progress has been made in relating scattering amplitudes in certain gravity theories to those in gauge theories — a correspondence dubbed the double copy. Recently, double copies have also been realized in a classical setting, as maps between exact solutions of gauge theories and gravity. We present here a novel map between a certain class of real, exact solutions of Einstein’s equations and self-dual solutions of the flat-space vacuum Maxwell equations. This map, which we call the Newman-Penrose map, is well-defined even for non-vacuum, non-stationary spacetimes, providing a systematic framework for exploring gravity solutions in the context of the double copy that have not been previously studied in this setting. To illustrate this, we present here the Newman- Penrose map for the Schwarzschild and Kerr black holes, and Kinnersley’s photon rocket.

Highlights

  • Tree level [2], appear to hold at loop level [3, 6,7,8,9,10], and are widely believed to hold to all orders in perturbation theory [11, 12]

  • In this work we introduce the Newman-Penrose map — a novel map, closely related to the classical double copy, that associates a self-dual solution of the vacuum Maxwell equations to certain Kerr-Schild spacetimes that need be neither stationary nor pure vacuum

  • The Newman-Penrose map defined in the previous subsection is, a priori, independent of the usual Kerr-Schild double copy which we reviewed in section 2.1, and one would not necessarily expect there to be any clear relationship between the real gauge fields associated with each prescription

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Summary

The classical double copy

We briefly review the Kerr-Schild classical double copy, and summarize the result for Schwarzschild spacetime. We review the zeroth and single copy relating solutions in gauge theory to bi-adjoint scalar theory. Of the self-dual double copy [20], the formalism of which parallels some of the framework introduced here

The Kerr-Schild double copy
The self-dual double copy
Newman-Penrose formalism for Kerr-Schild spacetimes
Shear-free and geodesic conditions
The Newman-Penrose map
General procedure
Examples
The Schwarzschild black hole
The Kerr black hole
Kinnersley’s photon rocket
15.1 Notation 1 What can kbe?
Discussion
Spinors
Kerr’s theorem
From flat-space to Kerr-Schild backgrounds: the Kerr-Wilson trick
B Spinorial realization of the Newman-Penrose map
C Details of the Kerr metric
Generating the Kerr-Schild form of the metric from Φ
Other coordinate systems
Full Text
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