Solar reflection of light dark matter with heavy mediators
  The direct detection of sub-GeV dark matter particles is hampered by their
low energy deposits. If the maximum deposit allowed by kinematics falls below
the energy threshold of a direct detection experiment, it is unable to detect
these light particles. Mechanisms that boost particles from the galactic halo
can therefore extend the sensitivity of terrestrial direct dark matter searches
to lower masses. Sub-GeV and sub-MeV dark matter particles can be efficiently
accelerated by colliding with thermal nuclei and electrons of the solar plasma
respectively. This process is called 'solar reflection'. In this paper, we
present a comprehensive study of solar reflection via electron and/or nuclear
scatterings using Monte Carlo simulations of dark matter trajectories through
the Sun. We study the properties of the boosted dark matter particles, obtain
exclusion limits based on various experiments probing both electron and nuclear
recoils, and derive projections for future detectors. In addition, we find and
quantify a novel, distinct annual modulation signature of a potential solar
reflection signal which critically depends on the anisotropies of the boosted
dark matter flux ejected from the Sun. Along with this paper, we also publish
the corresponding research software.
