A Gravitino-rich Universe

TL;DR

This paper explores the role of gravitinos in early universe cosmology, suggesting a gravitino-rich scenario that impacts baryogenesis and dark matter, especially under high-scale supersymmetry.

Contribution

It proposes a cosmological model where the universe is gravitino-rich, affecting entropy, baryon asymmetry, and dark matter production, with implications for high-scale supersymmetry.

Findings

Universe can be gravitino-dominated with entropy dilution.

Baryon asymmetry and dark matter are independent of reheating temperature.

Wino-like neutralino is a viable dark matter candidate.

Abstract

The gravitino may well play an important role in cosmology, not only because its interactions are Planck-suppressed and therefore long-lived, but also because it is copiously produced via various processes such as particle scatterings in thermal plasma, and (pseudo) modulus and inflaton decays. We study a possibility that the early Universe was gravitino-rich from various aspects. In particular, a viable cosmology is possible, if high-scale supersymmetry is realized in nature as suggested by the recent discovery of the standard-model like Higgs boson of mass about 125-126 GeV. We find that the Universe can be even gravitino-dominated, in which case there will be an entropy dilution by the gravitino decay. If the gravitino abundance is proportional to the reheating temperature, both the maximal baryon asymmetry in leptogenesis and the dark matter from the gravitino decay become independent of the reheating temperature. The dark matter candidate is the Wino-like neutralino, whose mass is suppressed compared to the anomaly-mediation relation.