Cold, warm, and composite (cool) cosmic string models

Abstract

The dynamical behaviour of a cosmic string is strongly affected by any reduction of the effective string tension T below the constant value, T = m 2 say, that typifies a simple, longitudinally Lorentz invariant Goto-Nambu type string model, where m is a fixed mass scale determined by the internal structure of an underlying Nielsen-Olesen type vacuum vortex. Such a reduction of tension occurs in the standard “warm” cosmic string model in which the effect of thermal perturbations of a simple Goto-Nambu model is represented by an effective tension T given in terms of the corresponding effective temperature, Θ say, by T 2 = m 2(m 2 − 1 3 πΘ 2) . A qualitatively similar though analytically more complicated tension reduction phenomenon occurs in “cold” conducting cosmic string models of the kind whose existence was first proposed by Witten, where the role of the temperature is played by an effective mass or chemical potential μ that is constructed as the scalar magnitude of the energy momentum covector obtained as the gradient of the phase ϕ of a bosonic condensate in the core of the vacuum vortex. The present article describes the construction and essential mechanical properties of a new category of composite “cool” cosmic string models that are intermediate between these “warm” and “cold” limit cases. These composite models are the string analogues of the standard Landau model for a two-constituent finite temperature superfluid, and as such involve two independent currents interpretable as that of the entropy on the one hand and that of the bosonic condensate on the other. It is surmised that the stationary (in particular ring) equilibrium states of such “cool” cosmic strings may be of cosmologicl significance.