  Motivated by the recent XENON1T results, we explore various new physics
models that can be discovered through searches for electron recoils in
O(keV)-threshold direct-detection experiments. First, we consider the
absorption of light bosons, either as dark matter relics or being produced
directly in the Sun. In the latter case, we find that keV mass bosons produced
in the Sun provide an adequate fit to the data but are excluded by stellar
cooling constraints. We address this tension by introducing a novel
Chameleon-like axion model, which can explain the excess while evading the
stellar bounds. We find that absorption of bosonic dark matter provides a
viable explanation for the excess only if the dark matter is a dark photon or
an axion. In the latter case, photophobic axion couplings are necessary to
avoid X-ray constraints. Second, we analyze models of dark matter-electron
scattering to determine which models might explain the excess. Standard
scattering of dark matter with electrons is generically in conflict with data
from lower-threshold experiments. Momentum-dependent interactions with a heavy
mediator can fit the data with dark matter mass heavier than a GeV but are
generically in tension with collider constraints. Next, we consider dark matter
consisting of two (or more) states that have a small mass splitting. The
exothermic (down)scattering of the heavier state to the lighter state can fit
the data for keV mass splittings. Finally, we consider a subcomponent of dark
matter that is accelerated by scattering off cosmic rays, finding that dark
matter interacting though an O(100 keV)-mass mediator can fit the data. The
cross sections required in this scenario are, however, typically challenged by
complementary probes of the light mediator. Throughout our study, we implement
an unbinned Monte Carlo analysis and use an improved energy reconstruction of
the XENON1T events.
