Baryon asymmetry of the universe and neutrino physics

In this thesis I have presented the findings of my research pursued during my Ph.D. study. The purpose of this thesis was to study different theoretical ideas in high energy physics model building addressed primarily towards understanding of one of the great mysteries of modern particle physics and cosmology; the Baryon Asymmetry (BA) of the universe (matter-antimatter asymmetry), and the close connection of this latter to Neutrino Physics. We concentrate on three of the most popular mechanisms to generate BA; realized in different ways: Baryogenesis via Leptogenesis, Soft Leptogenesis, and Resonant Leptogenesis. In the first chapter, we calculate BA induced in the decay of right-handed neutrinos in a class of minimal left-right symmetric models (LRSUSY). In these models, which assume low energy supersymmetry, the Dirac neutrino mass matrix has a determined structure. As a result, lepton asymmetry is calculable in terms of measurable low energy neutrino parameters. By numerically solving the Boltzmann equations we show that adequate BA is generated in these models in complete agreement with recent NASA high precision measurements. Furthermore, we make predictions on the light neutrino oscillation parameters, which can be tested in next generation neutrino experiments. In the second chapter, we discuss a more recent idea; Soft Leptogenesis. This time, we study the effect of the interactions of the SU(2) R gauge boson WR on the generation of the BA. B--L violation occurs when LRSUSY is broken by the VEV vR of the B--L = -2 triplet scalar field Delta c(1,1,3,-2), which gives Majorana masses to the r.h sneutrino, and lepton number is violated in their decay n&d5;R1 → e˜Rud¯, mediated by the right handed gauge boson WR, can dominate the traditional process nR → L&phis;† which drives Leptogenesis. We show that the requirement of unconventionally small B-term is no longer needed. In addition, we include RGE and SUSY breaking effect to naturally account for the complex order 1 phase as dictated by the success of the scenario. The mass of r.h sneutrino can be Mn&d5;∼MW R ∼ (109 - 1010) GeV. In the third chapter we turn our attention to Neutrino Physics. We present a predictive model of inverted neutrino mass hierarchy based on Le - Lmu - Ltau combined with an S2 permutation symmetry in the neutrino sector. Our analysis shows an interesting correlation between the mixing angles: sin2 q12 = 1/2 1-tan2 q13tanq13 cos delta, predicting q13 ≥ 0.13, and 0 ≤ delta ≤ 45°. Resonant Leptogenesis is discussed since the model involves two quasi-degenerate r.h.n, successfully generating adequate BA.