New Sources of Gravitational Waves during Inflation

TL;DR

This paper demonstrates that particle or string sources during inflation can produce detectable gravitational waves, which may dominate over quantum fluctuations, implying tensor mode detection doesn't directly measure the inflationary Hubble scale.

Contribution

It introduces a mechanism for generating inflationary gravitational waves from sources other than quantum fluctuations, expanding the understanding of possible signals.

Findings

Particle or string sources can produce dominant tensor modes during inflation.

Detection of tensor modes does not necessarily indicate the inflationary Hubble scale.

The effect is consistent with inflationary constraints and can occur at low potential energy.

Abstract

We point out that detectable inflationary tensor modes can be generated by particle or string sources produced during inflation, consistently with the requirements for inflation and constraints from scalar fluctuations. We show via examples that this effect can dominate over the contribution from quantum fluctuations of the metric, occurring even when the inflationary potential energy is too low to produce a comparable signal. Thus a detection of tensor modes from inflation does not automatically constitute a determination of the inflationary Hubble scale.