Domain wall constraints on the doublet left-right symmetric model from pulsar timing array data

Abstract

Recent evidence of a stochastic gravitational wave (GW) background found by NANOGrav and other pulsar timing array (PTA) collaborations has inspired many studies looking for possible sources. We consider the hypothesis that the GW signature is produced by domain walls (DWs) arising in the doublet left-right symmetric model (DLRSM) due to the spontaneous breaking of the discrete parity symmetry. We show that the DW network consists of two types of DWs, namely Z2 and LR DWs, and solve the kink equations to obtain the parametric dependence of the surface tension in the two cases. We argue that the Z2 DWs are unstable due to higher surface tension, leading to a stable network consisting only of LR DWs. Considering the GW signal from the DLRSM DW model with and without the contribution from supermassive black hole binaries, we perform a Bayesian analysis using the PTA data to estimate the posterior distribution and identify best-fit parameter ranges. The PTA data favors a parity-breaking scale of O(105) GeV, and a biased potential Vbias∼(O(100) MeV)4. The model with only DLRSM DWs is slightly favored over the model where additional supermassive black hole binaries contribution is considered. Published by the American Physical Society 2025