Eliminating the eta-problem in SUGRA Hybrid Inflation with Vector Backreaction

TL;DR

This paper demonstrates that gauge field backreaction in supergravity hybrid inflation creates a new attractor solution, resolving the eta-problem by enabling slow-roll inflation on steep potentials and maintaining a mildly red spectral index.

Contribution

It introduces a novel inflationary attractor in supergravity driven by vector backreaction, providing a generic solution to the eta-problem and aligning predictions with observations.

Findings

Backreaction induces a new inflationary attractor.

Spectral index of curvature perturbations is 0.97-0.98.

Observable anisotropy requires tuning of gauge coupling.

Abstract

It is shown that, when the inflaton field modulates the gauge kinetic function of the gauge fields in supergravity realisations of inflation, the dynamic backreaction leads to a new inflationary attractor solution, in which the inflaton's variation suffers additional impedance. As a result, slow-roll inflation can naturally occur along directions of the scalar potential which would be too steep and curved to support it otherwise. This provides a generic solution to the infamous eta-problem of inflation in supergravity. Moreover, it is shown that, in the new inflationary attractor, the spectral index of the generated curvature perturbations is kept mildly red despite eta of order unity. The above findings are applied to a model of hybrid inflation is supergravity with a generic Kaehler potential. The spectral index of the generated curvature perturbations is found to be 0.97 - 0.98, in excellent agreement with observations. The gauge field can play the role of the vector curvaton after inflation but observable statistical anisotropy requires substantial tuning of the gauge coupling.