Hunting for Dark Matter in Anisotropies of the Gamma-ray Sky: Predictions and First Observational Results from Fermi-LAT

Eiichiro Komatsu

May 23, 2012

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Abstract: Can we use the Fermi satellite like WMAP? In 2006, S. Ando and I proposed to use anisotropies in the gamma-ray background (not CMB!) as a smoking-gun signature of annihilation of dark matter particles in the universe. The idea is simple: since dark matter traces the large-scale structure of the universe, the emission from dark matter must be anisotropic, and its spatial pattern is predictable. The use of anisotropy (especially the power spectrum) was new to the gamma-ray community, so I teamed up with the Fermi-LAT team to look for this signature. Here, we report on the first detection of anisotropy in the diffuse gamma-ray background measured by Fermi-LAT. We find that the detected signal is very likely due to unresolved blazers. Subtracting this signal, we can place a fairly stringent upper limit on the residual anisotropy signal, which would then put constraints on dark matter properties.