Minimizing under relaxed symmetry constraints: Triple and $N$-junctions

Abstract

We consider a nonnegative potential $W:{\mathbb{R}}^2\to \mathbb{R}$ invariant under the action of the rotation group $C_N$ of the regular polygon with $N$ sides, $N\ge 3$. We assume that $W$ has $N$ nondegenerate zeros and prove the existence of a $N$-junction solution to the vector Allen-Cahn equation. The proof is variational and is based on sharp lower and upper bounds for the energy and on a new pointwise estimate for vector minimizers.

41 pages, 8 figures