Light dark matter versus astrophysical constraints
  Hints of direct dark matter detection coming from the DAMA, CoGeNT
experiments point toward light dark matter with isospin-violating and possibly
inelastic couplings. However an array of astrophysical constraints are rapidly
closing the window on light dark matter. We point out that if the relic density
is determined by annihilation into invisible states, these constraints can be
evaded. As an example we present a model of quasi-Dirac dark matter,
interacting via two U(1) gauge bosons, one of which couples to baryon number
and the other which kinetically mixes with the photon. Annihilation is
primarily into "dark neutrinos" that do not mix with the SM, but which could
provide a small component of dark radiation. The model could soon be tested by
several experiments searching for such light gauge bosons, and we predict that
both could be detected. The model also requires a fourth generation of quarks,
whose existence might increase the production cross section of Higgs bosons at
the Tevatron and LHC.
