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≳10¹⁶ GeV if m_N > m_WR, and m_WR≳2×10⁵ GeV(m_N/10² GeV)^¾ if m_N < m_WR, where m_N is the mass of the lightest right-handed neutrino. A better bound m_WR≳3×10⁶ GeV (m_N/10² GeV)^⅔ is obtained if leptogenesis occurs at T > m_WR. We show also that the m_N > m_WR option is excluded in a supersymmetric theory with gravitinos.