Marco Gorghetto; Edward Hardy; Giovanni Villadoro · 2021 · SciPost Physics
Paper
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.
Analysis
This paper investigates the contribution of string defects during the scaling regime to the QCD axion dark matter abundance, suggesting a significant number of axions and a stronger lower bound on the QCD axion mass.
Discovery
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