Supergravity can reconcile dark matter with lepton number violating neutrino masses

Supersymmetry offers a cold dark matter candidate, provided that lepton number is {\em not violated by an odd number of units}. On the other hand, lepton number violation by even (two) units gives us an attractive mechanism of neutrino mass generation. Here we offer an explanation of this, in a supergravity framework underlying a supersymmetric scenario, the essential feature being particles carrying lepton numbers, which interact only gravitationally with all other known particles. It is shown that one can have the right amount of $\Delta L = 2$ effect giving rise to neutrino masses, whereas the lifetime for $\Delta L = 1$ decays of the lightest supersymmetric particle can be prolonged beyond the present age of the universe.