Coupled currents in cosmic strings
  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.
