Towards a precision calculation of N <sub>eff</sub> in the Standard Model. Part III. Improved estimate of NLO contributions to the collision integral
Marco Drewes, Yannis Georis, Michael Klasen, Luca Paolo Wiggering, Yvonne Y. Y. Wong
Abstract
Abstract We compute the dominant QED correction to the neutrino-electron interaction rate in the vicinity of neutrino decoupling in the early universe, and estimate its impact on the effective number of neutrino species N eff in cosmic microwave background anisotropy observations. We find that the correction to the interaction rate is at the sub-percent level, consistent with a recent estimate by Jackson and Laine. Relative to that work we include the electron mass in our computations, but restrict our analysis to the enhanced t -channel contributions. The fractional change in N eff SM due to the rate correction is of order 10 -5 or below, i.e., about a factor of 30 smaller than that recently claimed by Cielo et al., and below the nominal computational uncertainties of the current benchmark value of N eff SM = 3.0440 ± 0.0002. We therefore conclude that aforementioned number remains to be the state-of-the-art benchmark for N eff SM in the standard model of particle physics.