WIMPless Dark Matter from an AMSB Hidden Sector with No New Mass
  Parameters
  We present a model with dark matter in an anomaly-mediated supersymmetry
breaking hidden sector with a U(1)xU(1) gauge symmetry. The symmetries of the
model stabilize the dark matter and forbid the introduction of new mass
parameters. As a result, the thermal relic density is completely determined by
the gravitino mass and dimensionless couplings. Assuming non-hierarchical
couplings, the thermal relic density is ~ 0.1, independent of the dark matter's
mass and interaction strength, realizing the WIMPless miracle. The model has
several striking features. For particle physics, stability of the dark matter
is completely consistent with R-parity violation in the visible sector, with
implications for superpartner collider signatures; also the thermal relic's
mass may be ~ 10 GeV or lighter, which is of interest given recent direct
detection results. Interesting astrophysical signatures are dark matter
self-interactions through a long-range force, and massless hidden photons and
fermions that contribute to the number of relativistic degrees of freedom at
BBN and CMB. The latter are particularly interesting, given current indications
for extra degrees of freedom and near future results from the Planck
observatory.
