Inflation and Monopoles in Supersymmetric SU(4)_c x SU(2)_L x SU(2)_R
  We show how hybrid inflation can be successfully realized in a supersymmetric model with gauge group G_{PS}= SU(4)_c x SU(2)_L x SU(2)_R. By including a non-renormalizable superpotential term, we generate an inflationary valley along which G_{PS} is broken to the standard model gauge group. Thus, catastrophic production of the doubly charged magnetic monopoles, which are predicted by the model, cannot occur at the end of inflation. The results of the cosmic background explorer can be reproduced with natural values (of order 10^{-3}) of the relevant coupling constant, and symmetry breaking scale of G_{PS} close to 10^{16} GeV. The spectral index of density perturbations lies between unity and 0.9. Moreover, the mu-term is generated via a Peccei-Quinn symmetry and proton is practically stable. Baryogenesis in the universe takes place via leptogenesis. The low deuterium abundance constraint on the baryon asymmetry, the gravitino limit on the reheat temperature and the requirement of almost maximal mu neutrino - tau neutrino mixing from SuperKamiokande can be simultaneously met with mu-neutrino, tau-neutrino and heaviest Dirac neutrino masses determined from the large angle MSW resolution of the solar neutrino problem, the SuperKamiokande results and SU(4)_c symmetry respectively. 
R. Jeannerot (ICTP,Trieste), S. Khalil (U.Autonoma de Madrid & U. Ain   Shams), G. Lazarides (Aristotle U. of Thessaloniki),...