Dark Nucleosynthesis: Cross-sections and Astrophysical Signals

TL;DR

This paper explores dark matter bound-state formation, providing generic formulas for cross-sections, analyzing their implications for indirect detection signals, and examining the validity of factorization assumptions in strongly-coupled dark sectors.

Contribution

It introduces generic formulas for dark matter bound-state formation involving photon and gauge boson emission, and assesses the factorization approximation's validity in these processes.

Findings

Bound-state formation can produce detectable gamma-ray signals.

Factorization often breaks down due to nuclear potential effects.

Minimal DM quintuplet signals are consistent with current bounds.

Abstract

We investigate dark matter bound-state formation and its implication for indirect-detection experiments. We focus on the case where dark matter is a baryon of a strongly-coupled dark sector and provide generic formulae for the formation of shallow nuclear bound states on emission of photons, and W and Z gauge bosons. These processes can occur via electric and magnetic transitions, and give rise to indirect signals that are testable in monochromatic and diffuse photon measurements by Fermi and HESS. We also study the validity of factorizing the bound-state formation cross section into a short-distance nuclear part multiplied by Sommerfeld-enhancement factors. We find that the short-distance nuclear potential often violates factorization, modifying in particular the location of the peaks associated with zero-energy bound states. Finally we revisit bound-state formation of a (weakly-coupled) Minimal DM quintuplet including isospin-breaking effects, and find it gives rise to indirect-detection signals that are compatible with current bounds.