Thermal Axion Production at Low Temperatures: A Smooth Treatment of the

We study thermal axion production around the confinement scale. At higher temperatures, we extend current calculations to account for the masses of heavy quarks, whereas we quantify production via hadron scattering at lower temperatures. Matching our results between the two opposite regimes provides us with a continuous axion production rate across the QCD phase transition. We employ such a rate to quantify the axion contribution to the effective number of neutrino species.

Automated summary

This study investigates the mechanism of thermal axion production around the confinement scale. By considering the masses of heavy quarks at higher temperatures and quantifying production via hadron scattering at lower temperatures, a continuous axion production rate across the QCD phase transition is obtained. Such a rate is then used to quantify the contribution of axions to the effective number of neutrino species.