Testing Lorentz invariance of dark matter

TL;DR

This paper investigates how deviations from Lorentz invariance in dark matter could be constrained using cosmological data, revealing effects on structure growth and potential bounds on Lorentz violation.

Contribution

It introduces a model with a dynamical vector field to represent Lorentz violation in dark matter and analyzes its impact on cosmic structure formation.

Findings

Scale-dependent enhancement in large-scale structure growth

Scale-dependent bias between dark matter and baryons

Potential to bound Lorentz violation at the percent level

Abstract

We study the possibility to constrain deviations from Lorentz invariance in dark matter (DM) with cosmological observations. Breaking of Lorentz invariance generically introduces new light gravitational degrees of freedom, which we represent through a dynamical timelike vector field. If DM does not obey Lorentz invariance, it couples to this vector field. We find that this coupling affects the inertial mass of small DM halos which no longer satisfy the equivalence principle. For large enough lumps of DM we identify a (chameleon) mechanism that restores the inertial mass to its standard value. As a consequence, the dynamics of gravitational clustering are modified. Two prominent effects are a scale dependent enhancement in the growth of large scale structure and a scale dependent bias between DM and baryon density perturbations. The comparison with the measured linear matter power spectrum in principle allows to bound the departure from Lorentz invariance of DM at the per cent level.