Gravitational waves at interferometer scales and primordial black holes in axion inflation

TL;DR

This paper explores the potential detection of a unique gravitational wave background from axion inflation across various experiments, which could reveal small-scale inflationary physics and primordial black hole formation.

Contribution

It introduces conditions under which axion inflation produces observable gravitational waves without conflicting with primordial black hole constraints.

Findings

Detectable gravitational wave signals are possible in current and future experiments.

The model can produce primordial black holes consistent with observational bounds.

Distinct properties like chirality and non-gaussianity help differentiate the signal.

Abstract

We study the prospects of detection at terrestrial and space interferometers, as well as at pulsar timing array experiments, of a stochastic gravitational wave background which can be produced in models of axion inflation. This potential signal, and the development of these experiments, open a new window on inflation on scales much smaller than those currently probed with Cosmic Microwave Background and Large Scale Structure measurements. The sourced signal generated in axion inflation is an ideal candidate for such searches, since it naturally grows at small scales, and it has specific properties (chirality and non-gaussianity) that can distinguish it from an astrophysical background. We study under which conditions such a signal can be produced at an observable level, without the simultaneous overproduction of scalar perturbations in excess of what is allowed by the primordial black hole limits. We also explore the possibility that scalar perturbations generated in a modified version of this model may provide a distribution of primordial black holes compatible with the current bounds, that can act as a seeds of the present black holes in the universe.