Cross-Correlation of Cosmic Shear and Extragalactic Gamma-ray
  Background: Constraints on the Dark Matter Annihilation Cross-Section
  We present the first measurement of the cross-correlation of weak
gravitational lensing and the extragalactic gamma-ray background emission using
data from the Canada-France-Hawaii Lensing Survey and the Fermi Large Area
Telescope. The cross-correlation is a powerful probe of signatures of dark
matter annihilation, because both cosmic shear and gamma-ray emission originate
directly from the same DM distribution in the universe, and it can be used to
derive constraints on dark matter annihilation cross-section. We show that the
measured lensing-gamma correlation is consistent with a null signal. Comparing
the result to theoretical predictions, we exclude dark matter annihilation
cross sections of <sigma v> =10^{-24}-10^{-25} cm^3 s^-1 for a 100 GeV dark
matter. If dark matter halos exist down to the mass scale of 10^-6 M_sun, we
are able to place constraints on the thermal cross sections <sigma v> ~ 3 x
10^{-26} cm^3 s^-1 for a 10 GeV dark matter annihilation into tau^{+} tau^{-}.
Future gravitational lensing surveys will increase sensitivity to probe
annihilation cross sections of <sigma v> ~ 5 x 10^{-26} cm^3 s^-1 even for a
100 GeV dark matter. Detailed modeling of the contributions from astrophysical
sources to the cross correlation signal could further improve the constraints
by ~ 40-70 %.
