The Galactic Center Excess from the Bottom Up
  It has recently been shown that dark-matter annihilation to bottom quarks
provides a good fit to the galactic-center gamma-ray excess identified in the
Fermi-LAT data. In the favored dark matter mass range $m\sim 30-40$ GeV,
achieving the best-fit annihilation rate $\sigma v \sim 5\times 10^{-26}$
cm$^{3}$ s$^{-1}$ with perturbative couplings requires a sub-TeV mediator
particle that interacts with both dark matter and bottom quarks. In this paper,
we consider the minimal viable scenarios in which a Standard Model singlet
mediates s-channel interactions only between dark matter and bottom quarks,
focusing on axial-vector, vector, and pseudoscalar couplings. Using simulations
that include on-shell mediator production, we show that existing sbottom
searches currently offer the strongest sensitivity over a large region of the
favored parameter space explaining the gamma-ray excess, particularly for
axial-vector interactions. The 13 TeV LHC will be even more sensitive; however,
it may not be sufficient to fully cover the favored parameter space, and the
pseudoscalar scenario will remain unconstrained by these searches. We also find
that direct-detection constraints, induced through loops of bottom quarks,
complement collider bounds to disfavor the vector-current interaction when the
mediator is heavier than twice the dark matter mass. We also present some
simple models that generate pseudoscalar-mediated annihilation predominantly to
bottom quarks.
