On the coupling of vector fields to the Gauss-Bonnet invariant

TL;DR

This paper explores a model where a massive vector field coupled to the Gauss-Bonnet invariant during inflation could act as a curvaton, aiming to avoid instabilities and maintain isotropy in the early universe.

Contribution

It introduces a novel non-minimal coupling of a vector field to the Gauss-Bonnet invariant and analyzes its potential to serve as a stable curvaton during inflation.

Findings

The vector field can act as a curvaton without instabilities.

The coupling preserves large-scale isotropy.

The model offers a stable alternative to previous vector inflation theories.

Abstract

Inflationary models including vector fields have attracted a great deal of attention over the past decade. Such an interest owes to the fact that they might contribute to, or even be fully responsible for, the curvature perturbation imprinted in the cosmic microwave background. However, the necessary breaking of the vector field's conformal invariance during inflation is not without problems. In recent years, it has been realized that a number of instabilities endangering the consistency of the theory arise when the conformal invariance is broken by means of a non-minimal coupling to gravity. In this paper, we consider a massive vector field non-minimally coupled to gravity through the Gauss-Bonnet invariant, and investigate whether the vector can play the role of a curvaton while evading the emergence of instabilities and preserves the large-scale isotropy.