Helicity Decay to Baryons: The Cosmological Evolution of L_μ-L_τ Gauge Fields and Baryogenesis

We study baryogenesis from the post-inflationary decay of helical U(1)L_μ-L_τ gauge fields generated during axion inflation. Assuming that Schwinger pair production is suppressed during inflation, a large helicity-to-entropy ratio ηH can be generated while keeping the initial lepton asymmetry just after inflation negligible. After reheating, the dissipation of magnetic helicity sources a lepton asymmetry through the chiral anomaly, which is partially converted into a baryon asymmetry by electroweak sphaleron processes. We find that there are parameter spaces where the observed baryon asymmetry can be generated in both the turbulent and dissipation-dominated regimes of the U(1)L_μ-L_τ magnetic field evolution. The baryon asymmetry generation in the turbulent regime is, however, dominated by the pre-turbulent nearly frozen regime. We further find that the requirement of successful baryogenesis imposes stronger constraints on the inflationary Hubble parameter and the helicity density generated during axion inflation than the requirement for the gauge-field energy not to backreact on the inflaton dynamics.