EXISTENCE AND STABILITY OF SEMILOCAL STRINGS

It has recently been shown that a certain model field theory [which gives the Abelian Higgs model a global SU(2) symmetry by duplicating the scalar sector] possesses static finite-energy vortex solutions despite having a simply connected vacuum manifold. It is demonstrated here that they are stable or unstable according to whether m(s) is less than or greater than m(v) (where m(s) and m(v) are the masses of the Higgs and vector particles, respectively). At the boundary, m(s) = m(v) there is a two-parameter family of solutions all saturating a Bogomol'nyi bound. The relationship of the vortices to CPn sigma-model lumps is pointed out.