Kerr-Schild--Kundt Metrics are Universal

TL;DR

This paper demonstrates that Kerr-Schild--Kundt metrics are universal solutions to a wide class of gravity theories, offering potential backgrounds for high-energy quantum field theory.

Contribution

It extends the family of known universal metrics by proving that Kerr-Schild--Kundt metrics are universal solutions in generic gravity theories.

Findings

Kerr-Schild--Kundt metrics are universal solutions.

These metrics solve source-free covariant field equations.

They can serve as backgrounds for high-energy quantum field theory.

Abstract

We define (non-Einsteinian) universal metrics as the metrics that solve the source-free covariant field equations of generic gravity theories. Here, extending the rather scarce family of universal metrics known in the literature, we show that the Kerr-Schild--Kundt class of metrics are universal. Besides being interesting on their own, these metrics can provide consistent backgrounds for quantum field theory at extremely high energies.