Gravitational wave emission from metastable current-carrying strings in E6

We discuss E6 based extensions of the Standard Model (SM) containing two varieties of superheavy metastable cosmic strings (CSs) that respectively have neutral and electrically charged current carriers. We employ an extended version of the velocity-dependent one-scale (VOS) model, recently discussed by some authors, to estimate the gravitational wave (GW) spectrum emitted by metastable strings with a dimensionless string tension Gμ≈10−6 that carry a right-handed neutrino (RHN) current. We find that with a low to moderate amount of current, the spectrum is compatible with the LIGO O3 run and also consistent at the 1σ level with the recent PTA signals.