More Axions from Strings

Understand

We study the contribution to the QCD axion dark matter abundance that is produced by string defects during the so-called scaling regime.

• Clear evidence of scaling violations is found, the most conservative extrapolation of which strongly suggests a large number of axions from strings.
• In this regime, nonlinearities at around the QCD scale are shown to play an important role in determining the final abundance.
• The overall result is a lower bound on the QCD axion mass in the post-inflationary scenario that is substantially stronger than the naive one from misalignment.