Warm dark energy

TL;DR

This paper explores a string-inspired mechanism where axion fields coupled to gauge fields can drive late-time cosmic acceleration, analyzing its realization in supergravity models and the transition dynamics of the universe.

Contribution

It demonstrates the implementation of Anber and Sorbo's axion-gauge field mechanism in supergravity models and studies the universe's transition to accelerated expansion.

Findings

Gauge backreaction can slow axion motion sufficiently for acceleration.

The evolution exhibits oscillations around the steady-state solution.

Transition dynamics include stages of faster and slower axion roll.

Abstract

Motivated by some of the recent swampland conjectures, we study the implementation for the late time acceleration of the Universe of a mechanism developed by Anber and Sorbo in the context of primordial inflation, in which an axion field can slowly roll in a steep potential due to additional friction provided by its coupling to some U(1) gauge field. We first study the realization of this mechanism in N = 2 supergravity models resulting from string compactifications on Calabi--Yau manifolds. We then study the transition between matter domination and the axion domination, and show that indeed the backreaction of the produced gauge field can sufficiently slow the motion of the axion, so to produce the present accelerated era. We finally study the transition from a pre-inflationary matter or radiation domination to primordial inflation. In the regime that we could explore numerically, the evolution is characterized by stages of faster axion roll (and consequent bursts of gauge field amplification) intermitted by stages of slower roll, with a pattern that "oscillates'' about the steady state Anber and Sorbo solution, but that does not appear to relax to it.