Axionic extension of the Proca action

TL;DR

This paper extends the Proca action within a Cartan geometric framework by incorporating an axion field, demonstrating a de Sitter phase with stable tensor and vector fluctuations and analyzing scalar perturbations for stability.

Contribution

It introduces an axionic extension of the Proca action derived from the Gauss-Bonnet term in Cartan theory, with detailed stability analysis of perturbations.

Findings

Model admits a de Sitter expanding phase with healthy fluctuations.

Scalar sector has 4 degrees of freedom, with only one dynamical at high momenta.

Parameter space identified where all perturbations are stable.

Abstract

In the context of Cartan theory, we will show that the Proca action can be obtained from the Gauss-Bonnet action for a special choice of the torsion tensor. This in fact equivalent to the special case of the 4th vector Galileon Lagrangian. The theory will then be promoted to contain an axion field. It will be proved that the model admits de Sitter expanding phase with healthy tensor and vector fluctuations. The scalar sector has 4 degrees of freedom, but only one of them remains dynamical in the limit $k\rightarrow\infty$. We will analyze the scalar fluctuations in the small scales limit and obtain the parameter space of the theory in which all the perturbations remain healthy.