ccsd-00000737 (version 1) : 15 Oct 2003 NON-DOMINATING HEAVY NEUTRINO DARK MATTER K.M.BELOTSKY, M.YU.KHLOPOV Center for Cosmoparticle Physics ”Cosmion”, Miusskaya Pl. 4, 125047, Moscow, Russia Physics Department, Rome University La Sapienza, Ple A.Moro 2, 00185, Roma, Italy The evidences for the existence stable 4th neutrino with the mass about 50 GeV may shed light on the string phenomenology. Being subdominant form of the modern dark matter, 4th neutrino can still contribute significantly into direct and indirect effects of WIMPs in the Galaxy. The results of DAMA, EGRET and HEAT can find explantion in the framework of this hypothesis. 1 Evidences for 4th neutrino By definition, primordial stable particles survive to the present time and should be present in the modern Universe. The net effect of their existence is given by their contribution into the total cosmological density. They can dominate in the total density being the dominant form of cosmological dark matter, or they can represent its subdominant fraction. In the latter case more detailed analysis of their distribution in space, of their condensation in galaxies, of their capture by stars, Sun and Earth, as well as of the effects of their interaction with matter and of their annihilation provides more sensitive probes for their existence. In particular, hypothetical stable neutrinos of the 4th generation with the mass about 50 GeV are predicted to form the subdominant form of the modern dark matter, contributing less than 0,1 % to the total density 1 . However, direct experimental search for cosmic fluxes of weakly interacting massive particles (WIMPs) may be sensitive to the existence of such component, and may be even favors it 2 . The dependence on 4th neutrino mass of the factor ξ = ρ loc /ρ N (local density ρ loc enhancement relative to the cosmological one ρ N ), at which the results 2 are reproduced, is given on Fig.1. It was shown in 3 , 4 , 5 that annihilation of 4th neutrinos and their antineutrinos in the Galaxy can explain the galactic gamma-background, measured by EGRET in the range above 1 GeV. 4th neutrino annihilation inside the Earth 6 should lead to the flux of underground