  Cosmic strings can be created in the early universe during symmetry-breaking
phase transitions, such as might arise if the gauge structure of the standard
model is extended by additional U(1) factors at high energies. Cosmic strings
present in the early universe form a network of long horizon-length segments,
as well as a population of closed string loops. The closed loops are unstable
against decay, and can be a source of non-thermal particle production. In this
work we compute the density of WIMP dark matter formed by the decay of gauge
theory cosmic string loops derived from a network of long strings in the
scaling regime or under the influence of frictional forces. We find that for
symmetry breaking scales larger than 10^10 GeV, this mechanism has the
potential to account for the observed relic density of dark matter. For
symmetry breaking scales lower than this, the density of dark matter created by
loop decays from a scaling string network lies below the observed value. In
particular, the cosmic strings originating from a U(1) gauge symmetry broken
near the electroweak scale, that could lead to a massive Z' gauge boson
observable at the LHC, produce a negligibly small dark matter relic density by
this mechanism.
