Is the NANOGrav signal a hint of dS decay during inflation?

TL;DR

This paper explores the possibility that the NANOGrav gravitational wave signal could be evidence of de Sitter space decay during inflation, driven by phase transitions consistent with swampland conjectures.

Contribution

It proposes a novel mechanism where phase transitions during inflation produce a red-tilted gravitational wave background compatible with NANOGrav observations.

Findings

Gravitational waves from dS decay can match NANOGrav data.

Decaying dS during inflation leads to a red-tilted GW spectrum.

The model aligns with swampland conjectures.

Abstract

As suggested by the swampland conjectures, de Sitter (dS) space might be highly unstable if it exists at all. During inflation, the short-lived dS states will decay through a cascade of the first-order phase transition (PT). We find that the gravitational waves (GWs) yielded by such a PT will be "reddened" by subsequent dS expansion, which may result in a slightly red-tilt stochastic GWs background at low-frequency band, compatible with the NANOGrav 12.5-yr result.