On the inflationary interpretation of the nHz gravitational-wave background

Abstract

We construct a single-field model of inflation that achieves remarkable agreement with Planck and BICEP/Keck cosmological observations. The model, via the presence of an ultra-slow-roll phase, generates a sizable scalar-induced gravitational wave (GW) signal at nHz frequencies. We elucidate the distinctive features of this signal concerning its connection to the recent measurement of the low-frequency GW background reported by the NANOGrav collaboration.

Comments: 17 pages (in double-column format) and 11 figures; v2: minor changes, refs. added