Baryogenesis via lepton-number-violating scalar interactions.

We study baryogenesis through lepton number violation in left-right symmetric models. In these models the lepton number and CP violating interactions of the triplet higgs scalars can give rise to lepton number asymmetry through non-equilibrium decays of the SU(2)L triplet higgs and the right handed neutrinos. This in turn generates baryon asymmetry during the electroweak anomalous processes. Cosmological baryon excess can be generated from the initial condition B = 0 if there is out-of-equilibrium baryon number violation along with CP violation [1]. However, the sphaleron induced, anomalous electroweak, process will wash out all the (B−L) conserving baryon asymmetry [2] which is generated at the grand unified scale. The ratio nB nγ = (4− 7)× 10 required by the standard big-bang model, can then be explained if there were primordial (B − L) asymmetry. Since the lowest dimensional operators for the proton decay conserve (B − L), it is unlikely that grand unified theories can generate enough (B − L) asymmetry. Two interesting possibilities then remain open. In the first one the observed asymmetry is generated just after the electroweak phase transition [3]. In this case the electroweak phase transition has to be strongly first order so that after the transition the anomalous process is already too weak to erase the generated asymmetry. The second possibility is the one where (B−L) asymmetry is generated during the anomalous electroweak process. If there are lepton number violating, out-of-equilibrium, interactions which violate CP, then during the epoch when the (B + L) violating anomalous processes are in equilibrium in the universe, this lepton asymmetry can generate enough (B − L) asymmetry. Some time back Fukugita and Yanagida [4, 5, 6] proposed this possibility, where the right handed neutrinos decay into light leptons and antileptons in different proportions when CP is violated [7]. This lepton asymmetry in turn generates baryon asymmetry. They considered an extension of the