Coupled currents in cosmic strings

TL;DR

This paper investigates the micro and macrostructure of cosmic strings with two Abelian currents, revealing conditions under which they behave like single-current strings and providing models for their stability and dynamics.

Contribution

It introduces a comprehensive analysis of two-current cosmic strings, including a new macroscopic description and simplified models for their stability and behavior.

Findings

Most two-current strings are equivalent to single-current strings.

Stable two-current strings can be modeled with logarithmic or rational Lagrangians.

The microstructure depends on two state parameters, with an additional Lorentz-invariant parameter linking the currents.

Abstract

We first examine the microstructure of a cosmic string endowed with two simple Abelian currents. This microstructure depends on two state parameters. We then provide the macroscopic description of such a string and show that it depends on an additional Lorentz-invariant state parameter that relates the two currents. We find that in most of the parameter space, the two-current string is essentially equivalent to the single current-carrying string, i.e., only one field condenses onto the defect. In the regions where two currents are present, we find that as far as stability is concerned, one can approximate the dynamics with good accuracy using an analytic model based on either a logarithmic (on the electric side, i.e., for timelike currents) or a rational (on the magnetic side, i.e., for spacelike currents) worldsheet Lagrangian.