Dark Matter via Massive (bi-)Gravity

TL;DR

This paper explores relativistic dark matter models within bimetric gravity, aiming to replicate MOND at galactic scales and CDM at cosmological scales, while addressing ghost instabilities.

Contribution

It introduces a class of ghost-free bimetric gravity models with dual dark matter sectors coupled via an internal vector field, capable of explaining galactic and cosmological phenomena.

Findings

Identified ghost issues in previous models.

Proposed new ghost-free bimetric models.

Models can reproduce MOND and CDM behaviors.

Abstract

In this work we investigate the existence of relativistic models for dark matter in the context of bimetric gravity, used here to reproduce the modified Newtonian dynamics (MOND) at galactic scales. For this purpose we consider two different species of dark matter particles that separately couple to the two metrics of bigravity. These two sectors are linked together \textit{via} an internal $U(1)$ vector field, and some effective composite metric built out of the two metrics. Among possible models only certain classes of kinetic and interaction terms are allowed without invoking ghost degrees of freedom. Along these lines we explore the number of allowed kinetic terms in the theory and point out the presence of ghosts in a previous model. Finally, we propose a promising class of ghost-free candidate theories that could provide the MOND phenomenology at galactic scales while reproducing the standard cold dark matter (CDM) model at cosmological scales.