Fermi Gamma-ray Space Telescope

Search for Gamma-ray Emission from p-wave Dark Matter Annihilation in the Galactic Center

Regina Caputo
(C. Johnson, J. Shelton, S. Ritz)


Indirect searches for dark matter (DM) annihilation to Standard Model products generally assume a cross-section which is dominated by a term independent of velocity (s-wave annihilation). However, in many DM models an s-wave annihilation cross-section is absent or helicity suppressed making p-wave annihilation (proportional to the squared DM velocity) the leading contribution to the cross section. Indirect detection of such p-wave DM in galactic halos is difficult, due to the small DM average velocities compared to the time of DM freeze out. Near the region of influence of a central supermassive black hole, such as Sgr A*, however, DM can form a localized over-density known as a “spike”. In such spikes the DM is both concentrated in space and accelerated to higher velocities, thereby allowing the gamma-ray signature from its annihilations to potentially be detectable above the background. We use the Fermi Large Area Telescope to search for the gamma ray signature of p-wave annihilating DM from a spike around Sgr A* in the energy range 10-600 GeV. Such a signal would appear as a point source and would have a sharp line or box-like spectral features indicating a DM origin. We find no significant excess of gamma rays in this range, and we place upper limits on the flux in gamma-ray boxes originating from the Galactic Center. This result is interpreted in the context of different models of the DM density near Sgr A*.