A thermal neutrino interaction rate at NLO

The interaction rate of an ultrarelativistic active neutrino at a temperature below the electroweak crossover plays a role in leptogenesis scenarios based on oscillations between active neutrinos and GeV-scale sterile neutrinos. By making use of a Euclideanization property of a thermal light-cone correlator, we determine the $O(g)$ correction to such an interaction rate in the high-temperature limit $\pi T \gg m_W$, finding a $\sim 15 ... 40\%$ reduction. For a benchmark point, this NLO correction decreases the lepton asymmetries produced by $\sim 1\%$.