Speaker
Description
We study baryogenesis from a helical U(1){L\mu-L_\tau} gauge field generated during axion inflation. If Schwinger production is suppressed during inflation, a sizable magnetic helicity can survive reheating while the initial fermion asymmetry remains negligible. In the radiation-dominated era, finite conductivity gradually dissipates the helicity. Through the chiral anomaly, this produces muon- and tau-flavor asymmetries, which are partially converted into baryon number by electroweak sphalerons.
We follow the magnetic-field evolution using MHD scaling laws when advection dominates and an exponential solution of the diffusion equation when Ohmic dissipation dominates. We then solve the coupled Boltzmann equations for the Standard Model particle asymmetries, including Yukawa interactions, strong and weak sphalerons, and the chiral magnetic effect. For g_{L_\mu-L_\tau}=3\times10^{-4}, the observed baryon asymmetry can be obtained in both the Ohmic-diffusion regime and the high-magnetic-Reynolds-number regime. In the latter case, the field remains nearly frozen until close to electroweak sphaleron freeze-out, so the baryon asymmetry is generated before a developed turbulent inverse cascade sets in. We find that the baryon abundance is sensitive to the small fraction of helicity dissipated before sphaleron freeze-out and can therefore constrain the inflationary parameter space more strongly than the gauge-field energy bound.