Sneutrino cold dark matter with lepton-number violation

The tau sneutrino is proposed as a candidate for galactic halo dark matter, and as the cold dark matter (CDM) component of the universe. A lepton-number-violating sneutrino mass, <(nu)over tilde><(nu)over tilde>, splits the tau sneutrino into two mass eigenstates: <(nu)over tilde> --> <(nu)over tilde>(+/-). The absence of a Z<(nu)over tilde>(-)<(nu)over tilde>(-) coupling implies that the lighter mass eigenstate, <(nu)over tilde>(-), does not annihilate via the s-channel Z-exchange to a low cosmological abundance, and furthermore, halo sneutrinos do not scatter excessively in Ge detectors. For the majority of the relevant parameter space, the event rate in Ge detectors is greater than or equal to 10(-2) events/kg/day. The lepton number violation required for sneutrino CDM implies that the tau neutrino mass is m(nu tau)greater than or similar to 5 MeV, large enough to be excluded by B factory experiments. Events of the form l(+)l(-)E or jjE, with low m(ll) or m(jj), may be observed at LEP2. A seesaw mechanism is investigated as the origin for the lepton number violation, and several other cosmological and particle physics consequences of sneutrino CDM are discussed. (C) 1998 Elsevier Science B.V.