  If dark matter (DM) couples to a force carrier that is much lighter than
itself, then it may form bound states in the early universe and inside haloes.
While bound-state formation via vector emission is known to be efficient and
have a variety of phenomenological implications, the capture via scalar
emission typically requires larger couplings and is relevant to more limited
parameter space, due to cancellations in the radiative amplitude. However, this
result takes into account only the trilinear DM-DM-mediator coupling. Theories
with scalar mediators include also a scalar potential, whose couplings may
participate in the radiative transitions. We compute the contributions of these
couplings to the radiative capture, and determine the parameter space in which
they are important.
