Neutrino masses and Baryogenesis via Leptogenesis in the Exceptional Supersymmetric Standard Model.
PhD thesis, University of Glasgow.
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Neutrino oscillation experiments discover that (left-handed) neutrinos have masses much less than charged leptons and quarks in the Standard Model. One solution to the light
neutrino mass puzzle is the seesaw model where right-handed neutrinos are introduced with large Majorana masses. The heavy Majorana right-handed (RH) neutrinos lead to lepton
number violation in the early universe. They decay into either leptons or anti-leptons via Yukawa couplings. The CP asymmetries of these decays result in lepton number asymmetry in the universe. The lepton number asymmetry can be converted into baryon number asymmetry via the electroweak sphaleron process. This mechanism explains the
baryon asymmetry of universe problem and is called leptogenesis.
However, one ﬁnds that in order to generated enough baryon number in the universe, the reheating temperature, which is required to be of order of the lightest right-handed
neutrino mass, has to be higher than ∼ 10^9 GeV. The high reheating temperature would lead to the over-produced gravitinos in the universe, contrasting with the present observation. We investigate leptogenesis in the Exceptional Supersymmetric Standard Model. We ﬁnd that the extra Yukawa couplings would enhance the CP asymmetries of the RH neutrino decay drastically. And the evolution of lepton/baryon asymmetries is described by Boltzmann Equations. Numerical calculation of the Boltzmann Equations shows that a correct amount of baryon number in the universe can be achieved when the lightest right-handed neutrino mass is ∼ 10^7 GeV, and then the gravitino-over-production problem is avoided.
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