Sphaleron Conversion of Lepton Number to Baryon Number and Its Freeze-Out in a Bounce History

Electroweak sphalerons are the exchange bureau between lepton number and baryon number in the early universe: they erase B+L while conserving B-L, so that a primordial lepton asymmetry emerges from the electroweak era partly converted into baryons. This paper computes the conversion with the Standard Model factor B = (28/79)(B-L), equal to 0.354 of the stored B-L, and finds that matching the observed baryon yield requires a primordial B-L yield of 2.45e-10. A B-L yield of 1e-9 would overproduce baryons, giving eta = 2.50e-09. The sphaleron rate exceeds the expansion rate by a factor 5.59e+09 at 131 GeV and by 7.32e+05 at 1e6 GeV, so conversion is in equilibrium throughout the relevant era in both the contracting and expanding passes of a bounce history, and the final baryon number is set at the last freeze-out, on the expanding side. Computed from stated assumptions, not measured.