Phenomenology of Dark Matter via a Bimetric Extension of General Relativity

TL;DR

This paper introduces a bimetric gravity model with two dark matter species and an internal vector field, successfully reproducing both cosmological and galactic phenomena, including $ ext{Λ}$-CDM and MOND, while remaining consistent with solar system tests.

Contribution

It presents a novel relativistic dark matter model using bimetric gravity and an internal vector field, unifying cosmological and galactic scale observations.

Findings

Reproduces $ ext{Λ}$-CDM at cosmological scales.

Recovers MOND phenomenology at galactic scales.

Compatible with solar system tests of gravity.

Abstract

We propose a relativistic model of dark matter reproducing at once the concordance cosmological model $\Lambda$-Cold-Dark-Matter ($\Lambda$-CDM) at cosmological scales, and the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. To achieve this we postulate a non-standard form of dark matter, consisting of two different species of particles coupled to gravity via a bimetric extension of general relativity, and linked together through an internal vector field (a "graviphoton") generated by the mass of these particles. We prove that this dark matter behaves like ordinary cold dark matter at the level of first order cosmological perturbation, while a pure cosmological constant plays the role of dark energy. The MOND equation emerges in the non-relativistic limit through a mechanism of gravitational polarization of the dark matter medium in the gravitational field of ordinary matter. Finally we show that the model is viable in the solar system as it predicts the same parametrized post-Newtonian parameters as general relativity.