Detection of gamma rays from dark matter annihilation in the galactic center is one of the feasible techniques to search for dark matter. We evaluate the gamma-ray flux in the case that the dark matter has an electroweak $\mathrm{S}\mathrm{U}(2{)}_L$ charge. Such dark matter is realized in the minimal supersymmetric standard model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like neutralino. When the dark matter is heavy compared to the weak gauge bosons, the leading-order calculation of the annihilation cross sections in perturbation breaks down due to a threshold singularity. We take into account nonperturbative effects by using the nonrelativistic effective theory for the two-body states of the dark matter and its $\mathrm{S}\mathrm{U}(2{)}_L$ partner(s), and evaluate precise cross sections relevant to the gamma-ray fluxes. We find that the annihilation cross sections may be enhanced by several orders of magnitude due to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the annihilation cross sections in the MSSM may be changed by factors even when the mass is about 500 GeV. We also discuss sensitivities to gamma-ray signals from the galactic center in the GLAST satellite detector and the large Air Cerenkov Telescope arrays.

• Received 4 January 2005

DOI:https://doi.org/10.1103/PhysRevD.71.063528