Degenerate neutrinos and supersymmetric inflation

Abstract

A moderate extension of the minimal supersymmetric standard model which includes a U(1) B− L gauge group ( B and L being the baryon and lepton number) and a Peccei–Quinn symmetry, U(1) PQ , is presented. The hybrid inflationary scenario is automatic and `natural' in this model. The μ problem of the minimal supersymmetric standard model is solved by coupling the electroweak higgses to fields which break U(1) PQ . Baryon number conservation and, thus, proton stability are automatic consequences of a R-symmetry. Neutrinos are assumed to acquire degenerate masses ≈1.5 eV by coupling to SU(2) L triplet superfields, thereby providing the hot dark matter of the universe. The inflaton system decays into these triplets which, via their subsequent decay, produce a primordial lepton asymmetry later converted into the observed baryon asymmetry of the universe. The gravitino and baryogenesis constraints can be satisfied with `natural' values (∼10 −3) of the relevant coupling constants.