`Mass without mass' from thin shells in Gauss-Bonnet gravity

TL;DR

This paper derives and analyzes thin shell equations in Gauss-Bonnet gravity, revealing vacuum wormhole solutions that mimic mass without requiring exotic matter, thus expanding understanding of gravitational structures in higher curvature theories.

Contribution

It formulates junction conditions for thin shells in Gauss-Bonnet gravity and classifies vacuum shell solutions, including wormholes, that exhibit mass-like behavior without matter.

Findings

Vacuum thin shells can mimic mass in asymptotic regions.

Wormhole solutions exist without exotic matter in Gauss-Bonnet gravity.

Three types of vacuum shell solutions are classified.

Abstract

Five tensor equations are obtained for a thin shell in Gauss-Bonnet gravity. There is the well known junction condition for the singular part of the stress tensor intrinsic to the shell, which we also prove to be well defined. There are also equations relating the geometry of the shell (jump and average of the extrinsic curvature as well as the intrinsic curvature) to the non-singular components of the bulk stress tensor on the sides of the thin shell. The equations are applied to spherically symmetric thin shells in vacuum. The shells are part of the vacuum, they carry no energy tensor. We classify these solutions of `thin shells of nothingness' in the pure Gauss-Bonnet theory. There are three types of solutions, with one, zero or two asymptotic regions respectively. The third kind of solution are wormholes. Although vacuum solutions, they have the appearance of mass in the asymptotic regions. It is striking that in this theory, exotic matter is not needed in order for wormholes to exist- they can exist even with no matter.