Sterile neutrino dark matter in B-L extension of the standard model and galactic 511 keV line

Sterile right-handed neutrinos can be naturally embedded in a low scale gauged U(1)(B-L) extension of the standard model. We show that, within a low reheating scenario, such a neutrino is an interesting dark matter candidate. We emphasize that if the neutrino mass is of the order of MeV, then it accounts for the measured dark matter relic density and also accommodates the observed flux of 511 keV photons from the galactic bulge.