Spin-2 dark matter from anisotropic Universe in bigravity

TL;DR

This paper explores how anisotropic early universe conditions in bigravity theories can produce spin-2 dark matter, which could be detectable via laser interferometry and explains dark matter abundance.

Contribution

It introduces a novel scenario where spin-2 dark matter is generated from anisotropic to isotropic universe transitions in bigravity models.

Findings

Stable fixed points classified in bigravity theories

Spin-2 dark matter produced during universe transition

Potential detectability of spin-2 dark matter by interferometers

Abstract

Bigravity is one of the natural extensions of general relativity and contains an additional massive spin-2 field which can be a good candidate for dark matter. To discuss the production of spin-2 dark matter, we study fixed point solutions of the background equations for axisymmetric Bianchi type-I Universes in two bigravity theories without Boulware-Deser ghost, i.e., Hassan-Rosen bigravity and Minimal Theory of Bigravity. We investigate the local and global stability of the fixed points and classify them. Based on the general analysis, we propose a new scenario where spin-2 dark matter is produced by the transition from an anisotropic fixed point solution to isotropic one. The produced spin-2 dark matter can account for all or a part of dark matter and can be directly detected by laser interferometers in the same way as gravitational waves.