Double layers in gravity theories

TL;DR

This paper explores the theoretical possibility of gravitational double layers in quadratic curvature gravity theories, presenting field equations, new physical quantities, and explicit examples, challenging previous assumptions about their impossibility.

Contribution

It introduces the concept of gravitational double layers in quadratic curvature theories, providing field equations and explicit examples that demonstrate their feasibility.

Findings

Double layers are possible in quadratic gravity theories.

New physical quantities associated with double layers are identified.

Explicit examples illustrate the physical plausibility of double layers.

Abstract

Gravitational double layers, unlike their classical electromagnetic counterparts, are thought to be forbidden in gravity theories. It has been recently shown, however, that they are feasible in, for instance, gravity theories with a Lagrangian quadratic in the curvature. This is surprising with many potential consequences and the possibility of new physical behaviours. While a clear interpretation seems elusive, several lines of research are open. I present the field equations for double layers, the new physical quantities arising, and several explicit examples.