A Signature of Cosmic Strings Wakes in the CMB Polarization
  We calculate a signature of cosmic strings in the polarization of the cosmic
microwave background (CMB). We find that ionization in the wakes behind moving
strings gives rise to extra polarization in a set of rectangular patches in the
sky whose length distribution is scale-invariant. The length of an individual
patch is set by the co-moving Hubble radius at the time the string is
perturbing the CMB. The polarization signal is largest for string wakes
produced at the earliest post-recombination time, and for an alignment in which
the photons cross the wake close to the time the wake is created. The maximal
amplitude of the polarization relative to the temperature quadrupole is set by
the overdensity of free electrons inside a wake which depends on the ionization
fraction $f$ inside the wake. The signal can be as high as $0.06 {\rm \mu K}$
in degree scale polarization for a string at high redshift (near recombination)
and a string tension $\mu$ given by $G \mu = 10^{-7}$.
