Solution
= Solution
For a uniform field the gradient term vanishes and minimization over $p=|\mathbf p|$ gives
$$
ap+bp^3=0.
$$
When $a<0$, the nonzero minimum has
$$
\boxed{p_0=\sqrt{-a/b}},
$$
while its direction is arbitrary by <rotational symmetry>. A sudden <quench> creates many independently oriented domains. Their mismatches contain gradients and <topological defects>, whose motion and pair annihilation are slow, so the uniform state is not reached promptly.