73 research outputs found
Flat Potential for Inflaton with a Discrete -invariance in Supergravity
We show that a very flat potential of inflaton required for a sufficient
inflation is naturally obtained in supergravity by imposing a discrete
-invariance . Several cosmological constraints on parameters in the
inflaton superpotential are derived. The reheating temperature turns out to be
GeV for the cases of =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 with mass exceeding the reheat temperature .
Once higher order processes are included, this statement is true for any
particle with renormalizable (gauge or Yukawa) interactions. This contribution
to the density often exceeds the contribution from thermal
production, leading to significantly stronger constraints on model parameters
than those resulting from thermal 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 ``-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
. 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
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