walls then disappear in the course of time as the true minimum spreads throughout space. Of course, in the context of the early Universe, there is an upper bound on the life-time of such walls if they are not to dominate the energy density of the Universe. As the standard theory of nucleosynthesis is in very good agreement with observations, one would also like that any such unstable domain walls do not influence it.

A restriction on the life-time of the unstable walls implies restriction on the parameters $\epsilon_1$ and $\epsilon_2$, which we now consider. \[Other parameters in eq. (1) are not constrained by such considerations from cosmology; the only other topological objects in the model are Skyrmions, which are supposed to be nucleons.\] Let us refer to the difference in the energy densities at $\theta = \pi$ and $\theta = 0$ as $\Delta \rho_V$. From eq. (23) we have $\Delta \rho_V = 2\epsilon_1 v$. One expects that the instability of domain walls becomes significant when the age of the Universe $t^*$ is such that the energy excess at the scale $t^*$ becomes comparable to the energy of the domain wall on the same scale [@av].

A good way to 