Turning off the Lights: How Dark is Dark Matter?

TL;DR

This paper examines observational constraints on charged dark matter, showing that small charges are unlikely to produce detectable signals due to galactic magnetic effects, despite potential scattering interactions.

Contribution

It introduces velocity-dependent scattering constraints and demonstrates that charged dark matter particles are evacuated from the galactic disk, reducing detection prospects.

Findings

Charge ratio $oldsymbol{rac{ ext{dark matter charge}}{ ext{electron charge}}} < 10^{-6}$ for 1 GeV mass

Charged dark matter is expelled from the galactic disk by magnetic fields and supernova shocks

Charged dark matter unlikely to be detected in current or upcoming experiments

Abstract

We consider current observational constraints on the electromagnetic charge of dark matter. The velocity dependence of the scattering cross-section through the photon gives rise to qualitatively different constraints than standard dark matter scattering through massive force carriers. In particular, recombination epoch observations of dark matter density perturbations require that $\epsilon$, the ratio of the dark matter to electronic charge, is less than $10^{-6}$ for $m_X = 1 GeV$, rising to $\epsilon < 10^{-4}$ for $m_X = 10 TeV$. Though naively one would expect that dark matter carrying a charge well below this constraint could still give rise to large scattering in current direct detection experiments, we show that charged dark matter particles that could be detected with upcoming experiments are expected to be evacuated from the Galactic disk by the Galactic magnetic fields and supernova shock waves, and hence will not give rise to a signal. Thus dark matter with a small charge is likely not a source of a signal in current or upcoming dark matter direct detection experiments.