f_{\pi}$ we find the lower bound to be $$\epsilon_1 > 3 \times 10^{-13} \;\; {\rm MeV}^3 \, .$$ As long as $\epsilon_1$ is larger than this the domain walls will disappear very quickly and will not affect the Universe in any significant way. Because the horizon is very small at that time, any density fluctuations generated by collapsing domain walls will also get wiped out quickly.

Clearly, the constraint on $\epsilon_1$ given by eq. (31) (and the corresponding constraint on $\epsilon_2$) is extremely weak. Since eq. (1) describes an effective theory anyway, it is safe to say that cosmology imposes no practical constraints on the parameters of this model.

High Energy Nuclear Collisions
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We now consider chiral symmetry breaking in the context of quark-gluon plasma formation in a heavy ion collision and the influence of misaligned chiral condensate on pion production. As we mentioned in the introduction, the possibility of coherent pion emission from extended domains is very interesting and has been a subject of many investigations recently [@bkt; @bd; @rw; @ggp; @lrg]. One of the problems in getting a clean signature is that such domains are expected to be very small [@ggp]. However, these investigations have been restricted 