Gravitational waves from p-form inflation

TL;DR

This paper investigates gravitational waves produced during p-form inflation, revealing differences in wave propagation speed and stability compared to scalar field inflation, with small field models being free of pathologies.

Contribution

It provides the first detailed analysis of gravitational wave behavior in p-form inflation, highlighting differences in propagation speed and stability issues.

Findings

Propagation speed of gravitational waves differs from unity in 2- and 3-form models.

Large field models exhibit negative squared speed, indicating instabilities.

Small field models are stable with negligible corrections to gravitational wave spectrum.

Abstract

Recently it was shown that an inflationary background can be realized by any $p$-form field non-minimally coupled to gravity. In this paper, we study gravitational waves generated during p-form inflation. Even though the background evolution is identical to that in conventional scalar field inflation, the behavior of gravitational waves is different in p-form inflation. In particular, we find that the propagation speed of gravitational waves differs from unity in 2- and 3-form inflationary models. We point out that the squared speed becomes negative in the large field models. The small field models are free from pathologies and the correction to the spectrum of gravitational waves turns out to be very small.