Gravitino overproduction in inflaton decay

Abstract

Most of the inflation models end up with non-vanishing vacuum expectation values of the inflaton fields φ in the true vacuum, which induce, in general, nonvanishing auxiliary field G φ for the inflaton potential in supergravity. We show that the presence of nonzero G φ gives 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 ∼ O(10) TeV. For several inflation models, we explicitly calculate the values of G φ and 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.

The decay of the inflaton in no-scale supergravity

“…So, heavier gravitinos and a lower reheating temperature as a result of a smaller decay rate of the inflaton via the gauge kinetic function, would lead to a larger branching ratio for gravitino production [15], making the problem more severe. Fortunately, gravitino production is suppressed in no-scale supergravity, and the problems mentioned above are avoided.…”

A cosmological upper bound on superpartner masses

“…The gravitino has a cosmological abundance determined by thermal scattering, freeze-in, and freeze-out and decay, and reaches thermal equilibrium, in accordance with (iv-A), only when it is very light. Additional sources for the gravitino production occurs in non-standard cosmological scenarios [8][9][10][11][12][13][14][15]. The gravitino abundance has been studied in detail for the case of weak-scale superpartners, for example leading to bounds on T R as a function of the gravitino mass [16].…”

Moduli-induced baryogenesis

“…Here we will provide analytic formulae which can be applied to a more generic mass spectrum of superparticles. Note that it was shown that the inflaton [26][27][28][29][30][31] as well as moduli [32][33][34][35] generically decays into a pair of gravitinos. Therefore the gravitino-dominated Universe can be realized in a broader scenario than originally assumed.…”

“…If the reheating temperature after inflation is high enough, the gravitino is copiously generated, and eventually dominates the Universe. In addition, the gravitino can also be produced by the inflaton decay [26][27][28][29][30][31]. In the typical mass spectra given in eq.…”