Is Self-Interacting Dark Matter Undergoing Dark Fusion?

TL;DR

This paper proposes dark matter fusion as a mechanism to address small-scale structure issues, predicting specific cross section behaviors and offering observational tests to distinguish it from other models.

Contribution

It introduces dark matter fusion as a novel relaxation process, with detailed predictions on cross sections and velocity dependence, advancing dark matter theory.

Findings

Dark fusion cross sections are estimated to be 0.1-1 barn.

Dark fusion predicts constant sigma v below galaxy cluster velocities.

Observations of galaxy groups can test the dark fusion hypothesis.

Abstract

We suggest that two-to-two dark matter fusion may be the relaxation process that resolves the small-scale structure problems of the cold collisionless dark matter paradigm. In order for the fusion cross section to scale correctly across many decades of astrophysical masses from dwarf galaxies to galaxy clusters, we require the fractional binding energy released to be greater than v^n ~ [10^{-(2-3)}]^n, where n=1,2 depends on local dark sector chemistry. The size of the dark-sector interaction cross sections must be sigma ~ 0.1-1 barn, moderately larger than for Standard Model deuteron fusion, indicating a dark nuclear scale Lambda ~ O(100 MeV). Dark fusion firmly predicts constant sigma v below the characteristic velocities of galaxy clusters. Observations of the inner structure of galaxy groups with velocity dispersion of several hundred kilometer per second, of which a handful have been identified, could differentiate dark fusion from a dark photon model.