Anisotropies in the gravitational wave background as a probe of the
  cosmic string network
  Pulsar timing arrays are one of the powerful tools to test the existence of
cosmic strings through searching for the gravitational wave background. The
amplitude of the background connects to information on cosmic strings such as
the tension and string network properties. In addition, one may be able to
extract more information on properties of cosmic strings by measuring
anisotropies in the gravitational wave (GW) background. In this paper, we
provide estimates of the level of anisotropy expected in the GW background
generated by cusps on cosmic strings. We find that the anisotropy level
strongly depends on the initial loop size $\alpha$, and thus we may be able to
put constraint on $\alpha$ by measuring the anisotropy of the GW background. We
also find that certain regions of the parameter space can be probed by shifting
the observation frequency of GWs.
