Axion string signatures II: A cosmological plasma collider
  We study early and late time signatures of both QCD axion strings and
hyperlight axion strings (axiverse strings). We focus on charge deposition onto
axion strings from electromagnetic fields and subsequent novel neutralizing
mechanisms due to bound state formation. While early universe signatures appear
unlikely, there are a plethora of late time signatures. Axion strings passing
through galaxies obtain a huge charge density, which is neutralized by a dense
plasma of bound state Standard Model particles forming a one dimensional
"atom". The charged wave packets on the string, as well as the dense plasma
outside, travel at nearly the speed of light along the string. These packets of
high energy plasma collide with a center of mass energy of up to $10^{9}$ GeV.
These collisions can have luminosities up to seven orders of magnitude larger
than the solar luminosity, and last for thousands of years, making them visible
at radio telescopes even when they occur cosmologically far away. The new
observables are complementary to the CMB observables for hyperlight axion
strings that have been recently proposed, and are sensitive to a similar
motivated parameter range.
