Department of Physics
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Item CP-violation in the mass matrix of heavy neutrinos(Elsevier, 1998-12) Vaidya, RishikeshWe discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry.Item Neutrino anomalies in a gauge mediated model with trilinear R violation(APS, 2002-02) Vaidya, RishikeshThe structure of neutrino masses and mixing resulting from trilinear R violating interactions is studied in the presence of gauge mediated supersymmetry breaking. Neutrino masses arise in this model at the tree level through the renormalization-group-induced vacuum expectation values of the sneutrinos and also through direct contribution at one loop. The relative importance of these contributions is determined by the values of the strong- and weak-coupling constants. In the case of purely λ′ couplings, the tree contribution dominates over the one-loop diagram. In this case, one simultaneously obtains atmospheric neutrino oscillations and quasivacuum oscillations of the solar neutrinos if all the λ′ couplings are assumed to be of similar magnitudes. If R parity violation arises from the trilinear λ couplings, then the loop-induced contribution dominates over the tree level. One cannot simultaneously explain the solar and atmospheric deficit in this case if all the λ couplings are of similar magnitude. This, however, becomes possible with hierarchical λ and we give a specific example of this.