Galactic gamma halo by heavy neutrino annihilations?

The diffused gamma halo around our Galaxy recently discovered by EGRET could be produced by annihilations of heavy relic neutrinos N (of fourth generation), whose mass is within a narrow range (M%/2 < mN < Mz). Neutrino annihilation in the halo may lead to either ultrarelativistic electron pairs whose Inverse Cornpton Scattering on infrared and optical galactic photons could be the source of observed GeV gamma rays. or prompt 100 MeV-l GeV photons (due to neutral pion secondaries) born by NN->Z-qq reactions. The consequeni gamma flux (10^-7 -10^-6 cm ^-2 s ^-1 sr ^1) is well comparable lo the EGRET observed one, and it is also compatible with the narrow window of neutrino mass 45 GeV < mN < 50 GeV, recently required to explain the underground DAMA signals.The presence of heavy neutrinos of fourth generation do not contribute much to solve the dark mailer problem of the Universe, but may be easily detectable by outcoming LEP II data.