Joint Theory Seminar
Speaker: Zacharia Chacko
Title: Lower Limits on the Strengths of Gamma Ray Lines from Dark Matter Annihilation
Host: Markus Luty
Room: 432
I will discuss the spectrum of gamma ray signals that arises from dark matter annihilation in the universe. I will focus on the large class of theories where the photon spectrum includes both diffuse gamma rays that arise from annihilation into Standard Model states at tree level, as well as monochromatic gamma rays arising from annihilation directly into two photons at the one loop level. In this class of theories I will obtain lower bounds on the ratio of the strength of the gamma ray line relative to the gamma ray continuum as a function of the dark matter mass and spin. These limits arise from the unitarity relation between the imaginary parts of the matrix elements of the loop diagrams that generate the line signal and the tree level amplitudes for dark matter annihilation into the intermediate states running in the loop and for their subsequent annihilation into two photons. These results are exact in the limit that dark matter annihilation is exclusively to a single Standard Model species, occurs through the lowest partial wave and respects CP. Away from this limit the bounds are approximate. These results agree with the known results in the literature in the case of the Minimal Supersymmetric Standard Model (MSSM).