Natural Chaotic Inflation in Supergravity and Leptogenesis

TL;DR

This paper presents a natural chaotic inflation model in supergravity built with a Nambu-Goldstone-like shift symmetry to eliminate the problematic exponential factor in the potential, and shows how small symmetry-breaking parameters in the superpotential can be natural in the tHooft sense. The dynamics yield chaotic inflation driven by the inflaton with a COBE-normalized mass scale of about $10^{13}$ GeV, followed by reheating at or below $10^9$ GeV to avoid the gravitino problem. The authors extend the model to realize leptogenesis via inflaton decay, where inflaton decays produce right-handed neutrinos whose CP-violating decays generate a lepton asymmetry that can account for the observed baryon density after sphaleron conversion, for a broad parameter range. They also discuss a Froggatt-Nielsen extension that modifies the mass and coupling hierarchies, preserving viability but shifting the quantitative outcomes, including the reheating temperature and generated asymmetry.

Abstract

We comprehensively investigate a chaotic inflation model proposed recently in the framework of supergravity. In this model, the form of Kähler potential is determined by a symmetry, that is, the Nambu-Goldstone-like shift symmetry, which guarantees the absence of the exponential factor in the potential for the inflaton field. Though we need the introduction of small parameters, the smallness of the parameters is justified also by symmetries. That is, the zero limit of the small parameters recovers symmetries, which is natural in the 't Hooft's sense. The leptogenesis scenario via the inflaton decay in this chaotic inflation model is also discussed. We find that the lepton asymmetry enough to explain the present baryon number density is produced for low reheating temperatures avoiding the overproduction of gravitinos.