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Gravitino Overproduction in Inflaton Decay

Masahiro Kawasaki, Fuminobu Takahashi, T. T. Yanagida

Abstract

Most of the inflation models end up with non-vanishing vacuum expectation values of the inflaton fields φin the true vacuum, which induce, in general, nonvanishing auxiliary field G_φfor the inflaton potential in supergravity. We show that the presence of nonzero G_φgives rise to inflaton decay into a pair of the gravitinos and are thereby severely constrained by cosmology especially if the gravitino is unstable and its mass is in a range of O(100) GeV \sim O(10) TeV. For several inflation models, we explicitly calculate the values of G_φand find that most of them are excluded or on the verge of being excluded for the gravitino mass in that range. We conclude that an inflation model with vanishing G_φ, typically realized in a chaotic inflation, is favored in a sense that it naturally avoids the potential gravitino overproduction problem.

Gravitino Overproduction in Inflaton Decay

Abstract

Most of the inflation models end up with non-vanishing vacuum expectation values of the inflaton fields φin the true vacuum, which induce, in general, nonvanishing auxiliary field G_φfor the inflaton potential in supergravity. We show that the presence of nonzero G_φgives rise to inflaton decay into a pair of the gravitinos and are thereby severely constrained by cosmology especially if the gravitino is unstable and its mass is in a range of O(100) GeV \sim O(10) TeV. For several inflation models, we explicitly calculate the values of G_φand find that most of them are excluded or on the verge of being excluded for the gravitino mass in that range. We conclude that an inflation model with vanishing G_φ, typically realized in a chaotic inflation, is favored in a sense that it naturally avoids the potential gravitino overproduction problem.

Paper Structure

This paper contains 7 sections, 27 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Inflaton decay into a pair of gravitinos
  3. Cosmological constraint on $G_{\phi}$
  4. Single field inflation model
  5. Hybrid inflation model
  6. Chaotic inflation model
  7. Conclusions

Figures (1)

  • Figure 1: Upper bound on the auxiliary field of the inflaton $G_\phi$ as a function of the inflaton mass $m_\phi$. The solid and dotted lines are for the hadronic branching ratio $B_h = 1$ and $10^{-3}$, respectively. We set $m_{3/2} = 1{\rm\, TeV}$. The typical values of $G_\phi$ and $m_\phi$ for the new and hybrid inflation models discussed in the text are also shown.