Could the primordial radiation be responsible for vanishing of topological defects?

We study the motion of domain walls in 1+1, 2+1 and briefly 3+1 d relativistic ϕ6 model with three equal vacua in the presence of radiation. We show that even small fluctuations can trigger a chain reaction leading to vanishing of the domain walls. Only one vacuum remains stable and domains containing other vacua vanish. We explain this phenomenon in terms of radiation pressure (both positive and negative). We construct an effective model which translates the fluctuations into additional term in the field theory potential. In case of two dimensional model we find a relation between the critical size of the bulk and amplitude of the perturbation.