Abstract
I present a complete calculation of the gamma-ray flux for neutralino annihilation into the two-photon final state. This channel can be quite important for the cosmological searching for the dark matter. I focus on the mSUGRA model to calculate the cross section of neutralino annihilation. In addition, I compare two different halo models, the core and the cuspy halo models, and discuss the spike corrections to them. If the uncertainty of the cosmological models such as halo models could be suppressed, then the validity of SUSY breaking models is discussable, especially if the cosmological telescopes detect the signal of the gamma-ray lines.