A Generalisation of the Nielsen-Olesen Vortex: Non-cylindrical Strings in a modified Abelian-Higgs Model

We modify the standard Abelian-Higgs model by introducing spatially-dependent cou-plings for the scalar and vector fields. We investigate static, non-cylindrically symmetric solutions of the resulting field equations and propose a pinch solution which interpolates between degenerate vacua along the string, labelled by ± |n|. This configuration corresponds to a vortex which shrinks to the Planck scale before re-emerging as an anti-vortex, resulting in the formation of a bead pair with one bead either side of the intersection. The solution is then topologically stable. A key assumption is that quantities such as phase and winding number, along with those which depend on them like the magnetic flux, become undefined at the Planck scale so that regions of opposite winding may be joined via a Planck-sized segment of neutral string. Similarities between this solution and the extra-dimensional windings of strings in type IIB string theory are discussed and a correspondence between field theory and string theory parameters is suggested. The spatial-dependence of the field couplings is found to have a natural interpretation in the string picture and results from the variation of the winding radius, giving rise to a varying (effective) string coupling. An interesting result is an estimate of the Higgs mass (at critical coupling) in terms of the parameters which define the Klebanov-Strassler geometry and which, in principle, may be constrained by cosmological observations.