Quest for Dark Matter with Cosmic Gamma-ray Observations

Abstract

The dark matter is now widely accepted as a major ingredient of the Universe and considered to constitute 6 times as much as the ordinary matter. However, the nature of the dark matter remains one of the biggest mysteries in the Universe. Since there is no plausible theory for the dark matter at this moment, we have variety of dark matter candidates, posing significant experimental challenges for detection and measurement of their properties. Among the dark matter candidates, Weakly Interacting Massive Particles (WIMPs) are the leading candidate since the scale of expected mass and cross section well matches the new physics expected in the weak scale such as supersymmetry and extra dimension. Gamma-ray observations aim at detecting gamma rays produced by WIMP annihilations or decays, and would provide direct constraints on the annihilation cross section which can be compared with the value expected from the thermal relic hypothesis. Current gamma-ray experiments exclude the WIMP mass below 20 GeV/c2 and future observations will be sensitive up to >10 TeV/c2 which covers a majority of the parameter space expected from new physics.