Non-Thermal Production of Dangerous Relics in the Early Universe

Many models of supersymmetry breaking, in the context of either supergravity or superstring theories, predict the presence of particles with weak scale masses and Planck-suppressed couplings. Typical examples are the scalar moduli and the gravitino. Excessive production of such particles in the early Universe destroys the successful predictions of nucleosynthesis. In particular, the thermal production of these relics after inflation leads to a bound on the reheating temperature, T_{RH} < 10^9 GeV. In this paper we show that the non-thermal generation of these dangerous relics may be much more efficient than the thermal production after inflation. Scalar moduli fields may be copiously created by the classical gravitational effects on the vacuum state. Consequently, the new upper bound on the reheating temperature is shown to be, in some cases, as low as 100 GeV. We also study the non-thermal production of gravitinos in the early Universe, which can be extremely efficient and overcome the thermal production by several orders of magnitude, in realistic supersymmetric inflationary models.Comment: 21 pages, 4 Postscript figure

Thermal and Non-Thermal Production of Gravitinos in the Early Universe

The excessive production of gravitinos in the early universe destroys the successful predictions of nucleosynthesis. The thermal generation of gravitinos after inflation leads to the bound on the reheating temperature, T_{RH}< 10^9 GeV. However, it has been recently realized that the non-thermal generation of gravitinos in the early universe can be extremely efficient and overcome the thermal production by several orders of magnitude, leading to much tighter constraints on the reheating temperature. In this paper, we first investigate some aspects of the thermal production of gravitinos, taking into account that in fact reheating is not instantaneous and inflation is likely to be followed by a prolonged stage of coherent oscillations of the inflaton field. We then proceed by further investigating the non-thermal generation of gravitinos, providing the necessary tools to study this process in a generic time-dependent background with any number of superfields. We also present the first numerical results regarding the non-thermal generation of gravitinos in particular supersymmetric models.Comment: 31 pages, 7 Postscript figures. New references adde

The Cosmological Moduli Problem and Preheating

Many models of supersymmetry breaking, in the context of either supergravity or superstring theories, predict the presence of particles with Planck-suppressed couplings and masses around the weak scale. These particles are generically called moduli. The excessive production of moduli in the early Universe jeopardizes the successful predictions of nucleosynthesis. In this paper we show that the efficient generation of these dangerous relics is an unescapable consequence of a wide variety of inflationary models which have a preheating stage. Moduli are generated as coherent states in a novel way which differs from the usual production mechanism during parametric resonance. The corresponding limits on the reheating temperature are often very tight and more severe than the bound of 10^9 GeV coming from the production of moduli via thermal scatterings during reheating.Comment: 17 pages, 5 Postscript figures, corrected some typo

Production of Massive Fermions at Preheating and Leptogenesis

We present a complete computation of the inflaton decay into very massive fermions during preheating. We show that heavy fermions are produced very efficiently up to masses of order 10^{17}-10^{18} GeV; the accessible mass range is thus even broader than the one for heavy bosons. We apply our findings to the leptogenesis scenario, proposing a new version of it, in which the massive right-handed neutrinos, responsible for the generation of the baryon asymmetry, are produced during preheating. We also discuss other production mechanisms of right-handed neutrinos in the early Universe, identifying the neutrino mass parameters for which the observed baryon asymmetry is reproduced.Comment: 29 pages, 4 figure

No evidence for gamma-ray halos around active galactic nuclei resulting from intergalactic magnetic fields

We analyze the gamma-ray halo around stacked AGNs reported in Ap.J.Lett., 2010, 722, L39. First, we show that the angular distribution of gamma-rays around the stacked AGNs is consistent with the angular distribution of the gamma-rays around the Crab pulsar, which is a point source for Fermi/LAT. This makes it unlikely that the halo is caused by an electromagnetic cascade of TeV photons in the intergalactic space. We then compare the angular distribution of gamma-rays around the stacked AGNs with the point-spread function (PSF) of Fermi/LAT and confirm the existence of an excess above the PSF. However, we demonstrate that the magnitude and the angular size of this effect is different for photons converted in the front and back parts of the Fermi/LAT instrument, and thus is an instrumental effect.Comment: accepted to A&