Oscillating Chiral Tensor Spectrum from Axionic Inflation

TL;DR

This paper investigates how axionic inflation models can produce oscillatory features in the primordial tensor spectrum, with potential detectability by future gravitational wave experiments, highlighting the role of gauge fields in enhancing these signals.

Contribution

It demonstrates that aligned chromo-natural inflation can generate detectable oscillations in the tensor spectrum due to gauge field effects, unlike single-field axion monodromy inflation.

Findings

Oscillations are suppressed in single-field axion monodromy inflation.

Chromo-natural inflation can produce sizable, detectable tensor oscillations.

Chiral gravitational waves are significantly enhanced in the gauge field-coupled model.

Abstract

We study the axionic inflation with a modulated potential and examine if the primordial tensor power spectrum exhibits oscillatory feature, which is testable with future space-based gravitational wave experiments such as DECIGO and BBO. In the case of the single-field axion monodromy inflation, it turns out that it is difficult to detect the oscillation in the spectrum due to suppression of the sub-Planckian decay constant of axion. On the other hand, in the case of aligned chromo-natural inflation where the axion is coupled to a SU(2) gauge field, it turns out that the sizable oscillation in the tensor spectrum can occur due to the enhancement of chiral gravitational waves sourced by the gauge field. We expect that this feature will be a new probe to axion phenomenologies in early universe through the chiral gravitational waves.