Shift Symmetry and Inflation in Supergravity

TL;DR

This paper explores supergravity inflation models with shift symmetry, demonstrating how mild symmetry breaking can alleviate the eta-problem and produce phenomenologically viable inflationary trajectories.

Contribution

It introduces a novel combination of shift symmetry, moduli stabilization, and symmetry breaking superpotentials to construct inflation models with curved trajectories in supergravity.

Findings

Shift symmetry creates a flat inflaton direction.

Mild symmetry breaking lifts the flatness, alleviating the eta-problem.

Models exhibit curved inflationary trajectories similar to mutated hybrid inflation.

Abstract

We consider models of inflation in supergravity with a shift symmetry. We focus on models with one moduli and one inflaton field. The presence of this symmetry guarantees the existence of a flat direction for the inflaton field. Mildly breaking the shift symmetry using a superpotential which depends not only on the moduli but also on the inflaton field allows one to lift the inflaton flat direction. Along the inflaton direction, the eta-problem is alleviated. Combining the KKLT mechanism for moduli stabilization and a shift symmetry breaking superpotential of the chaotic inflation type, we find models reminiscent of ``mutated hybrid inflation'' where the inflationary trajectory is curved in the moduli--inflaton plane. We analyze the phenomenology of these models and stress their differences with both chaotic and hybrid inflation.