Constraints on WIMP and Sommerfeld-Enhanced Dark Matter Annihilation
  from HESS Observations of the Galactic Center
  We examine the constraints on models of weakly interacting massive particle
(WIMP) dark matter from the recent observations of the Galactic center by the
High Energy Spectroscopic System (HESS) telescope. We analyze canonical WIMP
annihilation into Standard Model particle final states, including b/b-bar,
t/t-bar and W^+ W^-. The constraints on annihilation into b/b-bar is within an
order of magnitude of the thermal cross section at ~3 TeV, while the
tau^+/tau^- channel is within a factor of ~2 of thermal. We also study
constraints on Sommerfeld-enhanced dark matter annihilation models, and find
that the gamma-ray observational constraints here rule out all of the parameter
space consistent with dark matter annihilation interpretations of PAMELA and
the Fermi-LAT e^+/e^- spectrum, in specific classes of models, and strongly
constrains these interpretations in other classes. The gamma-ray constraints we
find are more constraining on these models, in many cases, than current relic
density, cosmic microwave background, halo shape and naturalness constraints.
