Stable solutions of inflation driven by vector fields

TL;DR

This paper develops a new class of vector-driven inflation models based on Generalized Proca Theory, successfully avoiding previous instabilities and providing stable, isotropic inflationary solutions with potential cosmological applications.

Contribution

It introduces a stable, isotropic vector inflation model extending Generalized Proca Theory, overcoming ghost and gradient instabilities present in earlier models.

Findings

Derived conditions for stable quasi de-Sitter solutions

Identified and demonstrated a simple stable vector inflation model

Broadened the scope of viable vector inflation scenarios

Abstract

Many models of inflation driven by vector fields alone have been known to be plagued by pathological behaviors, namely ghost and/or gradient instabilities. In this work, we seek a new class of vector-driven inflationary models that evade all of the mentioned instabilities. We build our analysis on the Generalized Proca Theory with an extension to three vector fields to realize isotropic expansion. We obtain the conditions required for quasi de-Sitter solutions to be an attractor analogous to the standard slow-roll one and those for their stability at the level of linearized perturbations. Identifying the remedy to the existing unstable models, we provide a simple example and explicitly show its stability. This significantly broadens our knowledge on vector inflationary scenarios, reviving potential phenomenological interests for this class of models.