Make Dark Matter Charged Again

TL;DR

This paper reevaluates constraints on dark matter charged under a dark U(1) gauge group, revealing viable parameter space for weak-scale charged dark matter and highlighting potential strong self-interactions affecting small galaxy dynamics.

Contribution

It identifies mitigating factors that weaken existing bounds, expanding the viable models of darkly-charged dark matter and exploring their implications for galaxy-scale phenomena.

Findings

Weakening of existing constraints allows for viable weak-scale charged dark matter models.

Dark matter self-interactions could be extremely large in dwarf galaxies.

A dynamical cutoff length scale limits heat transfer, affecting galaxy dynamics.

Abstract

We revisit constraints on dark matter that is charged under a $U(1)$ gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large, a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.