Chiral Primordial Gravitational Waves from Dilaton Induced Delayed Chromo-natural Inflation

TL;DR

This paper proposes a model of inflation involving a dilaton and axion coupled to an SU(2) gauge field, leading to the generation of detectable chiral primordial gravitational waves on small scales.

Contribution

It introduces a delayed chromo-natural inflation scenario driven by a dilaton and axion, producing chiral gravitational waves potentially observable by future detectors.

Findings

Chiral gravitational waves are generated on small scales.

The model is viable with an inert gauge field in early inflation.

Detectable gravitational wave signals could be observed by DECIGO, eLISA, and SKA.

Abstract

We study inflation driven by a dilaton and an axion, both of which are coupled to a SU(2) gauge field. We find that the inflation driven by the dilaton occurs in the early stage of inflation during which the gauge field grows due to the gauge kinetic function. When the energy density of magnetic fields catches up with that of electric fields, chromo-natural inflation takes over in the late stage of inflation, which we call delayed chromo-natural inflation. Thus, the delayed chromo-natural inflation driven by the axion and the gauge field is induced by the dilaton. The interesting outcome of the model is generation of chiral primordial gravitational waves on small scales. Since the gauge field is inert in the early stage of inflation, it is viable in contrast to the conventinal chromo-natural inflation. We find the parameter region where chiral gravitational waves are generated in a frequency range higher than nHz, which are potentially detectable in future gravitational wave interferometers and pulsar timing arrays such as DECIGO, eLISA and SKA.