Scale of SU(2) R symmetry breaking and leptogenesis

Abstract

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an SU(2) R gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that m N ≳10 16 GeV if m N > m W R , and m W R ≳2×10 5 GeV(m N/10 2 GeV) 3/4 if m N < m W R , where m N is the mass of the lightest right-handed neutrino. A better bound m W R ≳3×10 6 GeV(m N/10 2 GeV) 2/3 is obtained if leptogenesis occurs at T> m W R . We show also that the m N > m W R option is excluded in a supersymmetric theory with gravitinos.