Cosmological Evolution of Semilocal String Networks
  Semilocal strings -- a particular limit of electroweak strings -- are an
interesting example of a stable non-topological defect whose properties
resemble those of their topological cousins, the Abrikosov-Nielsen-Olesen
vortices. There is, however, one important difference: a network of semilocal
strings will contain segments. These are 'dumbbells' whose ends behave almost
like global monopoles that are strongly attracted to one another. While closed
loops of string will eventually shrink and disappear, the segments can either
shrink or grow, and a cosmological network of semilocal strings will reach a
scaling regime. We discuss attempts to find a "thermodynamic" description of
the cosmological evolution and scaling of a network of semilocal strings, by
analogy with well-known descriptions for cosmic strings and for monopoles. We
propose a model for the time evolution of an overall lengthscale and typical
velocity for the network as well as for its segments, and some supporting
(preliminary) numerical evidence.
