HEP Theory Journal Club

Interpretations of the galactic centre gamma-ray excess

Jonathan Cornell

McGill

Observations of the centre of our galaxy over a period of more than 5 years by the Fermi Large Area Telescope have revealed a robust excess of gamma rays at energies of a few GeV. As the shape of the spectrum of the excess is roughly equivalent with what is expected from annihilating dark matter, this has caused a great deal of excitement. However, it is possible that a more conventional astrophysical explanation could explain the excess, and there are difficulties in building dark matter models that avoid constraints caused by the lack of gamma rays observed from other dark matter rich objects. I will give an overview of some of the more popular explanations that have been given for the excess in the literature, starting with the astrophysical and then moving on to the possibility of dark matter annihilation. In particular, I will focus on the recently discussed possibility that the excess could be caused by dark matter whose self-annihilation cross section is velocity dependent, which would avoid the constraints on the dark matter annihilation rate from observations of dwarf spheroidal galaxies.