Evolution of magnetic fields in cosmic string wakes
  We study the evolution of magnetic fields in cosmic string wakes in a plasma
with a low resistivity. The initial magnetic field in the wake is modelled on
the magnetic fields that are generated by the motion of particles around cosmic
strings. The plasma is characterized by a high beta value. We find multiple
shock like structures developing in the wake of the string. We study the
detailed structure of the shocks formed and the evolution of the magnetic field
in the shock using a 2-D magnetohydrodynamic simulation. As expected, the
development of the magnetic field does not depend on the $\beta$ value. Our
results show that instead of a singe uniform shock forming behind the cosmic
string we have multiple shocks forming at short time intervals behind the
string. The presence of multiple shocks will definitely affect the
observational signatures of cosmic string wakes as these signatures depend upon
the temperature fluctuations generated by the shock. We also find that as the
shock moves away, the residual magnetic field left behind reconnects and
dissipates rapidly. The magnetic field around the string is thus very
localized. We find that magnetic field reconnections take place in cosmic
string wakes. This leads to the decrease of the magnetic field in the post
shock region.
