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Vortex Production at Phase Transitions in Nonrelativistic and Relativistic Media
We examine string (vortex) formation at a quench for a weakly-coupled global
U(1) theory when the excitation spectrum is non-relativistic. It is so similar
to vortex production in the corresponding relativistic plasma as to reinforce
arguments for the similarity of vorheptex production in the early universe and
in low-temperature many-body physics.Comment: 23 pages, replaced version - tex problems correcte
Statistical mechanics of strings with Y-junctions
We investigate the Hagedorn transitions of string networks with Y-junctions
as may occur, for example, with (p,q) cosmic superstrings. In a simplified
model with three different types of string, the partition function reduces to
three generalised coupled XY models. We calculate the phase diagram and show
that, as the system is heated, the lightest strings first undergo the Hagedorn
transition despite the junctions. There is then a second, higher, critical
temperature above which infinite strings of all tensions, and junctions, exist.
Conversely, on cooling to low temperatures, only the lightest strings remain,
but they collapse into small loops
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