Statistical Uncertainties of the $N_\text{DW} = 1$ QCD Axion Mass Window from Topological Defects

Understand

We review results from QCD axion string and domain wall simulations and propagate the associated uncertainties, including QCD uncertainties, into the calculation of the axion relic density.

• We compare two different sets of studies and, using cosmological constraints, perform statistical inference on the axion mass window in the post-inflationary Peccei-Quinn symmetry breaking scenario.
• For dark matter axions in recent simulations inferring a moderately infrared-dominated spectrum, this leads to a median dark matter axion mass of 0.50 meV, while the 95% credible interval at highest posterior density is between 0.48 and 0.52 meV.
• For alternative simulations including in addition string-domain wall decays (but with different overall inference on the spectrum), these numbers are 0.22 meV and [0.16, 0.27] meV.