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 $m_N\gtrsim 10^{16}$ GeV if $m_N>m_{W_R}$, and $m_{W_R}\gtrsim 3\times 10^{6}GeV(m_N/10^{2}GeV{)}^{2/3}$ if $m_N<m_{W_R}$, where $m_N$ is the mass of the lightest right-handed neutrino. However, the $m_N>m_{W_R}$ option is excluded in a supersymmetric theory with gravitinos.

Comments: 4 pages (Revtex); accepted for publication with small modifications; conclusions unchanged