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 `naturalʹ 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 `naturalʹ values (∼10−3) of the relevant coupling constants.
