  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.

High Energy Physics - Phenomenology;Cosmology and Nongalactic Astrophysics;Nuclear Theory