Exothermic Double-Disk Dark Matter
  If a subdominant component of dark matter (DM) interacts via long-range dark
force carriers it may cool and collapse to form complex structures within the
Milky Way galaxy, such as a rotating dark disk. This scenario was proposed
recently and termed "Double-Disk Dark Matter" (DDDM). In this paper we consider
the possibility that DDDM remains in a cosmologically long-lived excited state
and can scatter exothermically on nuclei (ExoDDDM). We investigate the current
status of ExoDDDM direct detection and find that ExoDDDM can readily explain
the recently announced ~3 sigma excess observed at CDMS-Si, with almost all of
the 90% best-fit parameter space in complete consistency with limits from other
experiments, including XENON10 and XENON100. In the absence of
isospin-dependent couplings, this consistency requires light DM with mass
typically in the 5-15 GeV range. The hypothesis of ExoDDDM can be tested in
direct detection experiments through its peaked recoil spectra, reduced annual
modulation amplitude, and, in some cases, its novel time-dependence. We also
discuss future direct detection prospects and additional indirect constraints
from colliders and solar capture of ExoDDDM. As theoretical proof-of-principle,
we combine the features of exothermic DM models and DDDM models to construct a
complete model of ExoDDDM, exhibiting all the required properties.
