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.Item Working group report: Neutrino and astroparticle physics(Springer, 2004-12) Layek, BiswanathThis is the report of neutrino and astroparticle physics working group at WHEPP-8. We present the discussions carried out during the workshop on selected topics in the above fields and also indicate progress made subsequently. The neutrino physics subgroup studied the possibilities of constraining neutrino masses, mixing and CPT violation in lepton sector from future experiments. Neutrino mass models in the context of Abelian horizontal symmetries, warped extra dimensions and in the presence of triplet Higgs were studied. Effect of threshold corrections on radiative magnification of mixing angles was investigated. The astroparticle physics subgroup focused on how various particle physics inputs affect the CMBR fluctuation spectrum, and on brane cosmology. This report also contains an introduction on how to use the publicly available code CMBFAST to calculate the CMBR fluctuations.