  Cosmic string networks are the best motivated relics of cosmological phase
transitions, being unavoidable in many physically plausible extensions of the
Standard Model. Most studies, including those providing constraints from and
forecasts of their observational signals, rely on assumptions of featureless
networks, neglecting the additional degrees of freedom on the string
worldsheet, e.g. charges and currents, which are all but unavoidable in
physically realistic models. An extension of the canonical velocity-dependent
one-scale model, accounting for all such possible degrees of freedom, has been
recently developed. Here we improve its physical interpretation by studying and
classifying its possible asymptotic scaling solutions, and in particular how
they are affected by the expansion of the Universe and the available energy
loss or transfer mechanisms. We find three classes of solutions. For
sufficiently fast expansion rates the charges and currents decay and one
asymptotes to the Nambu-Goto case, while for slower expansion rates they can
dominate the network dynamics. In between the two there is a third regime in
which the network, including its charge and current, reaches full scaling.
Under specific but plausible assumptions, this intermediate regime corresponds
to the matter-dominated era. Our results agree with, and significantly extend,
those of previous studies.
