Inflation, Strings, CMB anisotropies and Leptogenesis

In this talk, I shall focus on theories beyond the Standard Model which predict massive neutrinos. Hybrid inflation emerges naturally in these theories: the slow-rolling inflaton field is a gauge singlet which couples with a GUT Higgs field which triggers the end of inflation. In the standard scenario, spontaneous symmetry breaking takes place at the end of inflation at a scale $M$; $M_{GUT} > M > M_Z$ for inflation to solve the GUT monopole problem and cosmic strings always form at this intermediate scale. WMAP data constrain $M \in [10^{14.5}-10^{15.5}]$ GeV and the singlet-Higgs coupling $\kappa \in [10^{-7} - 10^{-2}]$. The spectral index $n_s \gtrsim 0.98$ in slight conflict with WMAP3. When the symmetry which is broken at the end of inflation is gauged $B-L$, both the inflaton and the strings decay into right-handed neutrinos. There are then two competing non-thermal scenarios for baryogenesis via leptogenesis which take place at the end of inflation, during reheating and from cosmic strings decay. Which of the two scenarios dominates depends on the inflaton-neutrino sector parameters.