Gravitational waves detectable in laser interferometers from axion-SU(2) inflation

TL;DR

This paper proposes a modified axion-SU(2) inflation model where gravitational waves are enhanced but remain within observational bounds, making them detectable by future gravitational wave observatories.

Contribution

It introduces a new inflationary scenario with gauge field VEVs that decay after horizon exit, allowing detectable GWs without conflicting with CMB constraints.

Findings

Enhanced gravitational waves within observational limits

Detectability of GWs by future observatories like BBO and ET

Viable parameter space for the model

Abstract

Chromo-natural inflation (CNI) is an inflationary model where an axion coupled with SU$(2)$ gauge fields acts as the inflaton. In CNI, the gauge fields have nonzero vacuum expectation values (VEVs), which results in the enhancement of gravitational waves (GWs). The original CNI is ruled out by the Planck observations due to the overproduction of GWs. In this work, we consider an inflationary model where the gauge fields acquire nonzero VEVs after the CMB modes exit the horizon. Moreover, we add to the model another field that dominates the universe and drives inflation after the axion starts to oscillate and the gauge field VEVs vanish. By performing numerical simulations, we find a parameter space where the enhanced GWs do not violate the CMB constraints and can be detected by the future GWs observations such as BBO and ET.