How to remedy the eta-problem of SUSY GUT hybrid inflation via vector backreaction

TL;DR

This paper introduces a supergravity inflation model where vector backreaction alleviates the eta-problem, enabling slow-roll inflation even with steep potentials, and predicts a spectral index consistent with observations.

Contribution

It proposes a novel vector backreaction mechanism in supergravity inflation that solves the eta-problem and maintains a realistic spectral index.

Findings

The model achieves slow-roll inflation despite steep potentials.

Spectral index of curvature perturbation is 0.97 - 0.98, matching data.

Vector field can generate statistical anisotropy, potentially observable.

Abstract

It is shown that, in supergravity models of inflation where the gauge kinetic function of a gauge field is modulated by the inflaton, we can obtain a new inflationary attractor solution, in which the roll-over of the inflaton suffers additional impedance due to the vector field backreaction. As a result, directions of the scalar potential which, due to strong Kaehler corrections, become too steep and curved to normally support slow-roll inflation can now naturally do so. This solves the infamous eta-problem of inflation in supergravity and also keeps the spectral index of the curvature perturbation mildly red despite eta of order unity. This mechanism is applied to a model of hybrid inflation in supergravity with a generic Kaehler potential. The spectral index of the curvature perturbation is found to be 0.97 - 0.98, in excellent agreement with data. The gauge field can act as vector curvaton generating statistical anisotropy in the curvature perturbation. However, this anisotropy could be possibly observable only if the gauge coupling constant is unnaturally small.