Global 21cm Absorption Signal from Superconducting Cosmic Strings
  Superconducting cosmic strings emit electromagnetic waves between the times
of recombination and reionization. Hence, they have an effect on the global
21cm signal. We compute the resulting absorption features, focusing on strings
with critical current, study their dependence on the string tension $\mu$, and
compare with observational results. For string tensions in the range of $G \mu
= 10^{-10}$, where $G$ is Newton's gravitational constant, there is an
interesting amplification of the two characteristic absorption features, one
during the cosmic dawn, $z \lesssim 30$, and the other during the cosmic dark
age, $z \sim 80$, the former being comparable in amplitude to what was observed
by the EDGES experiment.
