Induced Gravitational Waves from Ultra Slow-Roll Inflation and Pulsar Timing Arrays Observations

TL;DR

This paper explores how a specific inflationary model with an ultra slow-roll phase can produce gravitational waves consistent with recent pulsar timing array observations, and predicts testable signals at higher frequencies.

Contribution

It introduces a single field inflation model with an ultra slow-roll phase that explains the stochastic gravitational wave background observed by PTAs and predicts distinctive high-frequency signatures.

Findings

Model can fit current PTA data

Induced GWs depend on transition sharpness and USR duration

Predicts testable high-frequency GW signals

Abstract

The stochastic gravitational wave background (SGWB) detected recently by the pulsar timing arrays (PTAs) observations may have cosmological origins. In this work we consider a model of single field inflation containing an intermediate phase of ultra slow-roll. Fixing the amplitude of the peak of curvature perturbations by the PBHs bounds we calculate the gravitational waves (GWs) induced from the curvature perturbations enhanced during USR. The spectrum of the induced GWs depends on the sharpness of the transition from the USR phase to the final attractor phase as well as to the duration of the USR period. While the model can accommodate the current PTAs data but it has non-trivial predictions for the induced GWs on higher frequency ranges which can be tested by future observations.