A novel approach in the WIMP quest: cross-correlation of gamma-ray anisotropies and cosmic shear

The presence of large amounts of dark matter in the Universe is the expected source of two different cosmological effects: small gravitational distortions in the shapes of background galaxies (cosmic shear) and the cosmological emission of gamma rays. In fact, dark matter structures are responsible for the bending of light in the weak lensing regime, and those same cosmological objects can emit gamma-rays, either because they host astrophysical sources (active galactic nuclei or star-forming galaxies) or directly by dark matter annihilations or decays. Gamma-rays emission should therefore exhibit strong correlation with the cosmic shear signal. In this note we report on the computation of the cross-correlation angular power spectrum of cosmic shear and gamma-rays produced by the annihilation/decay of weakly interacting massive composing particle dark matter, as well as by astrophysical sources. We show that the shear/gamma-rays cross-correlation provides novel information on the composition of the extra-galactic gamma-ray background and can represent a potentially detectable signal by combining Fermi-LAT data with forthcoming galaxy surveys, like Dark Energy Survey and Euclid. At the same time, a detection of a cross-correlation signal would demonstrate that the weak lensing observables are indeed due to particle DM matter and not to possible modifications of General Relativity.