Abstract
We investigate a resonant leptogenesis scenario by quasi-degenerate righthanded neutrinos which have TeV-scale masses. Especially, we consider the case when two right-handed neutrinos are responsible to leptogenesis and the seesaw mechanism for active neutrino masses, and assume that the CP violation occurs only in the mixing matrix of active neutrinos. In this case the sign of the baryon asymmetry depends on the Dirac and Majorana CP phases as well as the mixing angle of the right-handed neutrinos. It is shown how the yield of the baryon asymmetry correlates with these parameters. In addition, we find that the effective neutrino mass in the neutrinoless double beta decay receives an additional constraint in order to account for the observed baryon asymmetry depending on the masses and mixing angle of right-handed neutrinos.
Highlights
BAU depends on the mixing matrix of active neutrinos U called as the Pontecorvo-MakiNakagawa-Sakata (PMNS) matrix [29, 30], and the CP violation due to the Dirac and/or Majorana phases in U can be an origin of the BAU
We have shown in the previous section that the successful scenario for resonant leptogenesis requires a certain range of the Majorana phase (i.e., α21 − α31 or α21 for the normal hierarchy (NH) or inverted hierarchy (IH) case) as well as the mixing angles of νR’s (i.e., Reω23 or Reω12 for the NH or IH case)
We have investigated the Standard Model extended by right-handed neutrinos, in which two νR’s are quasi-degenerate with TeV-scale masses
Summary
Let us explain the framework of the present analysis. We consider the Standard Model (SM) extended by three right-handed neutrinos νR I (I = 1, 2, 3) with the Lagrangian. FαI are Yukawa coupling constants and MM are Majorana mass matrix of right-handed neutrinos. We apply the seesaw mechanism for generating the suppressed masses of active neutrinos, and work in the parameter range MI |[MD]αI | = |FαI | H. Through the non-zero vacuum-expectation value of the Higgs field, they mix with active ones as νL α = Uαiνi + ΘαI NI with ΘαI = [MD]αI MI−1 This mixing induces the weak interaction of heavy neutral leptons suppressed by ΘαI. In this analysis we consider the case when only two right-handed neutrinos are responsible to the seesaw mechanism as well as leptogenesis for simplicity. In the present analysis we assume that the CP violation occurs only in the PMNS matrix and all the mixing parameters ωIJ are real. It is discussed whether two right-handed neutrinos whose masses are TeV-scale can produce a sufficient amount of the BAU or not
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