Cosmological Limits on Strong Dark Forces

TL;DR

This paper demonstrates how cosmological observations can impose strong constraints on models where dark matter interacts via long-range, Yukawa-coupled scalar forces, revealing rich dynamics and ruling out significant parameter space.

Contribution

It introduces a comprehensive analysis of dark matter with strong Yukawa-coupled scalar interactions, extending constraints beyond previous limits and exploring both attractive and repulsive forces.

Findings

Dark sector dynamics are richer than static Yukawa potential models.

Large regions of parameter space deviate from cold dark matter predictions.

Existing constraints rule out significant dark force interactions at sub-100 kpc scales.

Abstract

We showcase cosmology's ability to constrain long-range forces between dark matter particles. Specifically, we consider a fermionic dark matter interacting via a Yukawa-coupled light scalar, focusing on regimes where the dark forces are stronger than gravitational and yet unconstrained. We show that the dark sector dynamics, both at the background and perturbation levels, is far richer than what can be captured with just the static interparticle Yukawa potential. The background dynamics includes an attractor that funnels a wide range of initial conditions onto an evolution unique to each parameter space. In a large swath of parameter space beyond existing limits, the dark sector deviates drastically from cold dark matter in observable epochs. We rule out this parameter space using existing constraints on dark-sector equation of state and small-scale cosmic perturbations, thus setting the strongest constraints yet on dark matter self-interactions at length scales shorter than 100 kpc. In addition, we briefly discuss repulsive dark forces and place cosmological limits that are stricter than in the attractive case.