Baryon number freeze-out in the Standard Model, precisely
Abstract
Weak sphaleron transitions turn a lepton asymmetry of the Standard Model plasma in the early Universe into a baryon asymmetry, conserving baryon-minus-lepton number B−L and its individual flavored charges. A baryon asymmetry can thus also arise from flavored lepton asymmetries with vanishing B−L. Standard equilibrium calculations in the symmetric and broken phases are performed at constant temperature and hence neglect the fact that both the Higgs expectation value and the sphaleron rate vary as functions of temperature across the electroweak crossover. We derive a Boltzmann equation for the baryon number evolution across the crossover and calculate the freeze-out abundance including higher-order corrections to both the grand canonical partition function and the perturbative Higgs expectation value. This yields two sphaleron conversion factors: Csph = 0.3328(5) for B−L and ℱsph = 0.0279(19) for the flavored charges weighted by the charged-lepton Yukawa couplings.
Related
- Strange-quark-number-dependent response to partonic dynamics in baryon-rich Au+Au collisions
- Net-baryon number distributions and the QCD phase diagram
- Right-handed neutrino dark matter consistent with the generation of baryon number asymmetry
- Anomaly in baryon number
- Imprints of the nuclear liquid-gas phase transition on net-baryon number fluctuations
BibTeX
@misc{benso2026baryon,
title = {{Baryon number freeze-out in the Standard Model, precisely}},
author = {Cristina Benso and Dietrich Bödeker and Kohei Kamada and Kyohei Mukaida and Laura Sagunski and Philipp Schicho and Kai Schmitz},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.07467},
eprint = {2609.07467},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.07467},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Baryon number freeze-out in the Standard Model, precisely
AU - Cristina Benso
AU - Dietrich Bödeker
AU - Kohei Kamada
AU - Kyohei Mukaida
AU - Laura Sagunski
AU - Philipp Schicho
AU - Kai Schmitz
PY - 2026
DA - 2026/09/07
PB - arXiv
DO - 10.48550/arxiv.2609.07467
UR - https://arxiv.org/abs/2609.07467
AB - Weak sphaleron transitions turn a lepton asymmetry of the Standard Model plasma in the early Universe into a baryon asymmetry, conserving baryon-minus-lepton number B−L and its individual flavored charges. A baryon asymmetry can thus also arise from flavored lepton asymmetries with vanishing B−L. Standard equilibrium calculations in the symmetric and broken phases are performed at constant temperature and hence neglect the fact that both the Higgs expectation value and the sphaleron rate vary as functions of temperature across the electroweak crossover. We derive a Boltzmann equation for the baryon number evolution across the crossover and calculate the freeze-out abundance including higher-order corrections to both the grand canonical partition function and the perturbative Higgs expectation value. This yields two sphaleron conversion factors: C_sph = 0.3328(5) for B−L and ℱ_sph = 0.0279(19) for the flavored charges weighted by the charged-lepton Yukawa couplings.
ER -