# Pure double-layer bubbles in quadratic F(R) gravity

## TL;DR

This paper introduces a novel class of spherically symmetric bubble solutions in quadratic F(R) gravity, featuring pure double layers supported by thin shells, marking the first such example in gravitational theories.

## Contribution

It demonstrates the existence of pure double layers in quadratic F(R) gravity, expanding the understanding of junctions and layered structures in modified gravity theories.

## Key findings

- Pure double layers are possible with negative quadratic coefficients.
- Bubbles separate regions with different constant scalar curvatures.
- First example of a pure double layer in a gravitational theory.

## Abstract

We present a class of spherically symmetric spacetimes corresponding to bubbles separating two regions with constant values of the scalar curvature, or equivalently with two different cosmological constants, in quadratic F(R) theory. The bubbles are obtained by means of the junction formalism, and the matching hypersurface supports in general a thin shell and a gravitational double layer. In particular, we find that pure double layers are possible for appropriate values of the parameters of the model whenever the quadratic coefficient is negative. This is the first example of a pure double layer in a gravitational theory.