The 21cm Signature of a Cosmic String Loop
  Cosmic string loops lead to nonlinear baryon overdensities at early times,
even before the time which in the standard LCDM model corresponds to the time
of reionization. These overdense structures lead to signals in 21cm redshift
surveys at large redshifts. In this paper, we calculate the amplitude and shape
of the string loop-induced 21cm brightness temperature. We find that a string
loop leads to a roughly elliptical region in redshift space with extra 21cm
emission. The excess brightness temperature for strings with a tension close to
the current upper bound can be as high as 1 degree K for string loops generated
at early cosmological times (times comparable to the time of equal matter and
radiation) and observed at a redshift of z + 1 = 30. The angular extent of
these predicted "bright spots" is of the order 0.1 degree for a value of the
string tension equal to the current upper bound. These signals should be
detectable in upcoming high redshift 21cm surveys.
