Gravitational Waves from Domain Walls in Pulsar Timing Array Datasets

Understand

We present a model-independent search for the gravitational wave background from cosmic domain walls (DWs) in the NANOGrav 12.5 years dataset and International PTA Data Release 2.

• DWs that annihilate at temperatures $\sim 20-50~\text{MeV}$ with tensions $\sim (40-100~\text{TeV})^3$ provide as good a fit to both datasets as the astrophysical background from supermassive black hole mergers.
• DWs may decay into the Standard Model (SM) or a dark sector.
• In the latter case we predict an abundance $\Delta N_{\text{eff}}$ of dark radiation well within the reach of upcoming CMB surveys.