About electroweak domain walls in Majoron models

Abstract: Some time ago it was claimed in "Spontaneous Breaking of Lepton Number and Cosmological Domain Wall Problem" (Phys. Rev. Lett. 122, 151301 (2019)) that non perturbative instantons of the weak interaction $\text{SU}(2)\text{W}$ lead to the formation of domain walls in Majoron models owing to the anomaly of the spontaneously broken global lepton number $L$ symmetry $\text{U}(1)_L$ with respect to $\text{SU}(2)\text{W}$. We point out that it has long been known, that this effect can be completely rotated away unless there is a source of explicit $B+L$ breaking present, where $B$ denotes baryon number. We further estimate the tiny instanton induced Majoron mass from $B+L$ breaking and analyze the cosmological impact of such domain walls including possible finite temperature effects. In general this scenario does not lead to a cosmological catastrophe.