  The Sun may capture asymmetric dark matter (DM), which can subsequently form
bound-states through the radiative emission of a sub-GeV scalar. This process
enables generation of scalars without requiring DM annihilation. In addition to
DM capture on nucleons, the DM-scalar coupling responsible for bound-state
formation also induces capture from self-scatterings of ambient DM particles
with DM particles already captured, as well as with DM bound-states formed
in-situ within the Sun. This scenario is studied in detail by solving Boltzmann
equations numerically and analytically. In particular, we take into
consideration that the DM self-capture rates require a treatment beyond the
conventional Born approximation. We show that, thanks to DM scatterings on
bound-states, the number of DM particles captured increases exponentially,
leading to enhanced emission of relativistic scalars through bound-state
formation, whose final decay products could be observable. We explore
phenomenological signatures with the example that the scalar mediator decays to
neutrinos. We find that the neutrino flux emitted can be comparable to
atmospheric neutrino fluxes within the range of energies below one hundred MeV.
Future facilities like Hyper-K, and direct DM detection experiments can further
test such scenario.
