Flat Potential for Inflaton with a Discrete RR-invariance in Supergravity

We show that a very flat potential of inflaton required for a sufficient inflation is naturally obtained in $N=1$ supergravity by imposing a discrete $R$-invariance $Z_{n}$. Several cosmological constraints on parameters in the inflaton superpotential are derived. The reheating temperature turns out to be $(1-10^8)$GeV for the cases of $n$=3--10. Baryogenesis in this model is also discussed briefly.Comment: 15 pages and 1 figure(uudecoded), LaTeX, TU-45

Particle production and dissipative cosmic field

Large amplitude oscillation of cosmic field that may occur right after inflation and in the decay process of weakly interacting fields gives rise to violent particle production via the parametric resonance. In the large amplitude limit the problem of back reaction against the field oscillation is solved and the energy spectrum of created particles is determined in a semi-classical approximation. For large enough coupling or large enough amplitude the resulting energy spectrum is broadly distributed, implying larger production of high energy particles than what a simple estimate of the reheating temperature due to the Born formula would suggest

Production of massive stable particles in inflaton decay

We point out that inflaton decays can be a copious source of stable or long--lived particles $\chi$ with mass exceeding the reheat temperature $T_R$. Once higher order processes are included, this statement is true for any $\chi$ particle with renormalizable (gauge or Yukawa) interactions. This contribution to the $\chi$ density often exceeds the contribution from thermal $\chi$ production, leading to significantly stronger constraints on model parameters than those resulting from thermal $\chi$ production alone. For example, we all but exclude models containing stable charged particles with mass less than half the mass of the inflaton.Comment: 4 revtex pages, 1 figure (uses axodraw). Slightly modified for better clarification, few changes in references. Final verssion published in Phys. Rev. Let

Natural New Inflation in Broken Supergravity

We consider a natural new inflationary model in broken supergravity based on an R symmetry. The model predicts a concrete relation between the amplitude of primordial density fluctuations and the scale of supersymmetry breaking. The observed value of the density fluctuations is obtained for the gravitino mass of order the weak scale along with a power-law spectral index considerably less than one, which may be tested in future observations.Comment: 12 pages, late

Dynamical Tuning of the Initial Condition for New Inflation in Supergravity

We point out that for a class of `new inflation' models in supergravity the required initial value of the inflaton field is dynamically set if there is another inflation (`pre-inflation') before the `new inflation'. We study the dynamics of both inflatons by taking a hybrid inflation model for the `pre-inflation' as an example. We find out that our `new inflation' model provides reheating temperatures T_R \simeq 10 MeV - 10^4 GeV low enough to avoid the gravitino problem even in gauge-mediated supersymmetry-breaking models. We also construct a model where the scale for the `new inflation' is generated by nonperturbative dynamics of a supersymmetric gauge theory.Comment: 16 pages, late

Particle Production and Gravitino Abundance after Inflation

Thermal history after inflation is studied in a chaotic inflation model with supersymmetric couplings of the inflaton to matter fields. Time evolution equation is solved in a formalism that incorporates both the back reaction of particle production and the cosmological expansion. The effect of the parametric resonance gives rise to a rapid initial phase of the inflaton decay followed by a slow stage of the Born term decay. Thermalization takes place immediately after the first explosive stage for a medium strength of the coupling among created particles. As an application we calculate time evolution of the gravitino abundance that is produced by ordinary particles directly created from the inflaton decay, which typically results in much more enhanced yield than what a naive estimate based on the Born term would suggest.Comment: 23 pages + 13 figure

Baryogenesis and Gravitino Dark Matter in Gauge-Mediated Supersymmetry-Breaking Models

We discuss two cosmological issues in a generic gauge-mediated supersymmetry (SUSY)-breaking model, namely the Universe's baryon asymmetry and the gravitino dark-matter density. We show that both problems can be simultaneously solved if there exist extra matter multiplets of a SUSY-invariant mass of the order of the ``$\mu$-term'', as suggested in several realistic SUSY grand-unified theories. We propose an attractive scenario in which the observed baryon asymmetry is produced in a way totally independent of the reheating temperature of inflation without causing any cosmological gravitino problem. Furthermore, in a relatively wide parameter space, we can also explain the present mass density of cold dark matter by the thermal relics of the gravitinos without an adjustment of the reheating temperature of inflation. We point out that there is an interesting relation between the baryon asymmetry and the dark-matter density.Comment: 20 pages, 2 figure

New inflation in supergravity with a chaotic initial condition

We propose a self-consistent scenario of new inflation in supergravity. Chaotic inflation first takes place around the Planck scale, which solves the longevity problem, namely, why the universe can live much beyond the Planck time, and also gives an adequate initial condition for new inflation. Then, new inflation lasts long enough to generate primordial fluctuations for the large scale structure, which generally has a tilted spectrum with the spectral index $n_{s} < 1$. The successive decay of the inflaton leads to the reheating temperature low enough to avoid the overproduction of gravitinos in a wide range of the gravitino mass.Comment: 11 pages. To appear in Phys. Rev.

Leptogenesis with Almost Degenerate Majorana Neutrinos

We investigate the leptogenesis with almost degenerate neutrinos, in the framework of democratic mass matrix, which naturally explains the large mixing angles for neutrino oscillations as well as quark masses and mixing matrix. We find that the baryon asymmetry in the present universe is explained via the decays of right-handed neutrinos produced nonthermally by the inflaton decay. The model predicts neutrinoless double beta decays accessible in near future experiments.Comment: 17 pages, LaTeX, 2 figure