Axion string signatures: 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.

Automated summary

We study the early and late time signatures of QCD axion strings and hyperlight axion strings, focusing on charge deposition and neutralizing mechanisms. While early universe signatures appear unlikely, there are numerous late time signatures. Axion strings passing through galaxies obtain a large charge density, which is neutralized by bound state Standard Model particles. The charged wave packets on the string and the dense plasma outside travel at nearly the speed of light and can have collisions with high energies, making them visible at radio telescopes even when occurring cosmologically far away. These new observables are complementary to the recently proposed CMB observables for hyperlight axion strings and are sensitive to a similar parameter range.