Soft Leptogenesis as a Viable Model of Baryogenesis
Fong, Chee Sheng
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The fact that we live in a matter-antimatter asymmetric universe is a deep mystery which the Standard Model of particle physics falls short of explaining. Imposing supersymmetry on the Standard Model plus right-handed neutrinos with lepton-number-violating Majorana masses results in the stability of the Higgs mass under quantum corrections, small active neutrino masses and generation of baryon asymmetry of the universe (baryogenesis) through leptogenesis. If supersymmetry is realized in nature, it has to be broken. The existence of soft supersymmetry-breaking terms introduce additional CP violating sources which can be utilized in leptogenesis in a scenario termed soft leptogenesis. In the first part of this dissertation we study the contributions to CP violation in soft leptogenesis paying special attention to the role of thermal corrections. Using both field-theoretical and quantum mechanical approaches, we compute the CP asymmetries and conclude that for all soft supersymmetry-breaking sources of CP violation considered, an exact cancellation between the leading order asymmetries produced in the fermionic and bosonic channels occurs at T=0 and hence thermal effects are needed to prevent this cancellation. Motivated by the relevance of quantum effects in resonant leptogenesis, we further investigate the impact of the use of quantum Boltzmann equations in soft leptogenesis. Then we study the lepton flavor effects in the temperature range relevant for soft leptogenesis 10<super>5</super> GeV &le T &le <super>9<\super> GeV and show that they could enhance the efficiency of soft leptogenesis up to an order of 1000 from the unflavored scenario. This enhancement permits larger values of the required lepton-violating soft bilinear term up to a natural supersymmetric scale (TeV). Finally, we discuss the effective theory appropriate for studying soft leptogenesis at temperatures T > 10<super>7</super> GeV where the main source of B-L asymmetry is the CP asymmetry of a new anomalous R-charge. This results in baryogenesis through R-genesis with an efficiency that can be up to two orders of magnitude larger than in the usual estimates. Contrary to common belief, a sizable baryon asymmetry is generated also when thermal effects are neglected.