Phase transition during inflation and the gravitational wave signal at pulsar timing arrays

Understand

The gravitational wave (GW) signal offers a promising window into the dynamics of the early universe.

• The recent results from the pulsar timing arrays (PTAs) could be the first glimpse of such new physics.
• In particular, they could point to new details during inflation, which can not be probed by other means.
• We explore the possibility that the new results could come from the secondary GWs sourced by curvature perturbations, generated by a first-order phase transition during inflation.