Schwinger--Keldysh formulation of electromagnetic leptogenesis in an EFT framework

Abstract

Can the electromagnetic dipole interactions probed in precision experiments be the same interactions that generated the baryon asymmetry of the Universe? We address this question by formulating low-scale electromagnetic leptogenesis (EMLG) as a gauge-invariant EFT, rather than as a broken-phase dipole ansatz. The point is not only to connect leptogenesis to laboratory dipole observables, but first to test whether the dipole-dominated dynamics itself can satisfy the cosmological viability requirement. Starting from a softly broken $Z_2$ UV completion, we match onto the $ν$SMEFT dipole operators $O_{NB}$ and $O_{NW}$, run their Wilson coefficients to the electroweak scale, and construct the broken-phase dipole couplings to $γ$, $Z$, and $W^\pm$. The soft breaking keeps the ordinary Yukawa-mediated sector subleading, thereby isolating the electromagnetic mechanism. We find that the non-resonant hierarchical regime is structurally inefficient, while in the quasi-degenerate regime the self-energy contribution is resonantly enhanced and dipole-dominated EMLG can reproduce the observed baryon asymmetry for viable TeV-scale parameters. The same EFT pipeline maps the successful EMLG parameter space onto low-energy dipole observables, including charged-lepton flavor violation, electric dipole moments, and anomalous magnetic moments. Precision dipole searches can therefore constrain, discriminate, and potentially falsify an electromagnetic origin of baryogenesis.