Numerical simulations of necklaces in SU(2) gauge-Higgs field theory
  We perform the first numerical simulations of necklaces in a non-Abelian
gauge theory. Necklaces are composite classical solutions which can be
interpreted as monopoles trapped on strings, rather generic structures in a
Grand Unified Theory. We generate necklaces from random initial conditions,
modelling a phase transition in the early Universe, and study the evolution.
For all cases, we find that the necklace system shows scaling behaviour similar
to that of a network of ordinary cosmic strings. Furthermore, our simulations
indicate that comoving distance between the monopoles or semipoles along the
string asymptotes to a constant value at late times. This means that while the
monopole-to-string energy density ratio decreases as the inverse of the scale
factor, a horizon-size length of string has a large number of monopoles,
significantly affecting the dynamics of string loops. We argue that
gravitational wave bounds from millisecond pulsar timing on the string tension
in the Nambu-Goto scenario are greatly relaxed.
