Towards a precision calculation of N $_{eff}$ in the Standard Model. Part III. Improved estimate of NLO contributions to the collision integral
(2024) Journal of Cosmology and Astroparticle Physics — Vol. 06 (2024)
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- 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.
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Drewes, M., Georis, Y., & et al. (2024). Towards a precision calculation of N $_{eff}$ in the Standard Model. Part III. Improved estimate of NLO contributions to the collision integral. Journal of Cosmology and Astroparticle Physics, 06. https://doi.org/10.1088/1475-7516/2024/06/032 (Original work published 2024)