The CP(N-1) model on a Disc and Decay of a Non-Abelian String

We consider the role of quantum effects in the non-perturbative decay of non-abelian string with orientational moduli in non-supersymmetric D=4 gauge theory. To this aim the effective action in the $CP(N-1)$ model on a disc at large N has been calculated. It exhibits phase transition at some radius, the “wrong sign” Luscher term and large boundary boojum-like negative contribution. The effect of $\theta$ - term and the possibility of the spontaneous creation of the non-abelian string are briefly discussed.