$(L_e-L_{\mu}-L_{\tau})$ discrete symmetry for heavy right-handed neutrinos and degenerate leptogenesis

Abstract

The degenerate leptogenesis is studied when the degeneracy in two of the heavy right-handed neutrinos [the third one is irrelevant if $\mu -\tau $ symmetry is assumed] is due to $\bar{L}\equiv (L_{e}-L_{\mu}-L_{\tau}) $ discrete symmetry. It is shown that a sizeable leptogenesis asymmetry $(\epsilon \succsim 10^{-6}) $ is possible. The level of degeneracy required also predicts the Majorana phase needed for the asymmetry. Since it is the same phase, which appears in the double $\beta $% -decay and this prediction is testable. Implication of non-zero reactor angle $\theta_{13}$ are discussed. It is shown that the contribution from $% \sin ^{2}\theta_{13}$ to leptogenesis asymmetry parameter may even dominate.An accurate measument of $\sin ^{2}\theta_{13}$ would have important implications for the mass degeneracy of heavy right-handed neutrinos.