The Wouthuysen Field Absorption Trough in Cosmic Strings Wakes
  The baryon density enhancement in cosmic string wakes leads to a stronger
coupling of the spin temperature to the gas kinetic temperate inside these
string wakes than in the intergalactic medium (IGM). The Wouthuysen Field (WF)
effect has the potential to enhance this coupling to such an extent that it may
result in the strongest and cleanest cosmic string signature in the currently
planned radio telescope projects. Here we consider this enhancement under the
assumption that X-ray heating is not significant. We show that the size of this
effect in a cosmic string wake leads to a brightness temperature at least two
times more negative than in the surrounding IGM. If the SCI-HI [1, 2] or EDGES
[3, 4] experiment confirm a WF absorption trough in the cosmic gas, then cosmic
string wakes should appear clearly in 21 cm redshift surveys of z = 10 to 30.
