CHIRAL COSMIC STRINGS

We consider all global cosmic-string solutions of U(1) scalar field theory with a cylindrically symmetric energy density. These can be characterized as extrema of the field's energy for given angular and linear momenta. This string class comprises, apart from the well-known ordinary and rotating strings, twisted string configurations whose isophase surfaces twist as one moves along the axis, and lightlike-phase strings in which the twisted phase propagates at the speed of light parallel to the string axis. We rule out global strings whose isophase contours are spirals in a plane. We prove, in a unified way and for a broad class of scalar potentials, the stability of ordinary, rotating, and lightlike-phase strings with a unit winding number against small perturbations. Twisted strings are apparently unstable unless they are made into loops. Lightlike-phase strings are stable for causal rather than for topological reasons.