Hidden Sector Dark Matter Models for the Galactic Center Gamma-Ray
  Excess
  The gamma-ray excess observed from the Galactic Center can be interpreted as
dark matter particles annihilating into Standard Model fermions with a cross
section near that expected for a thermal relic. Although many particle physics
models have been shown to be able to account for this signal, the fact that
this particle has not yet been observed in direct detection experiments
somewhat restricts the nature of its interactions. One way to suppress the dark
matter's elastic scattering cross section with nuclei is to consider models in
which the dark matter is part of a hidden sector. In such models, the dark
matter can annihilate into other hidden sector particles, which then decay into
Standard Model fermions through a small degree of mixing with the photon, Z, or
Higgs bosons. After discussing the gamma-ray signal from hidden sector dark
matter in general terms, we consider two concrete realizations: a hidden photon
model in which the dark matter annihilates into a pair of vector gauge bosons
that decay through kinetic mixing with the photon, and a scenario within the
generalized NMSSM in which the dark matter is a singlino-like neutralino that
annihilates into a pair of singlet Higgs bosons, which decay through their
mixing with the Higgs bosons of the MSSM.
