Electromagnetic Leptogenesis -- an EFT-Consistent Analysis via Wilson Coefficients. Part II. Low-Scale, Resonant Regime

We study electromagnetic leptogenesis (EMLG) in the low-scale, resonant regime within a fully effective-field-theory (EFT)–consistent framework. Starting from a UV Lagrangian and performing a one-loop matching to obtain the gauge-invariant dipole operator $O_{NB}$ with its Wilson coefficient $C_{NB}$, we implement the Pilaftsis–Underwood resummation for the self-energy contributions to the CP asymmetries and evolve a flavour covariant transport system across the electroweak window. In the quasi-degenerate limit $M_m-M_i\simeq {\Gamma }_m\mathrm{/}2$, the CP-odd source acquires a Breit–Wigner–form enhancement whereas the washout saturates, with the freeze-out baryon asymmetry achieving $Y_B^{\mathrm{F}\mathrm{O}}\gtrsim {10}^{-10}$ across the strong-washout regime, comfortably above the observed value $Y_B^{\mathrm{o}\mathrm{b}\mathrm{s}}\simeq 8.7\times {10}^{-11}$. This establishes resonant EMLG at $O(100)\mathrm{G}\mathrm{e}\mathrm{V}$ as a viable EFT-based mechanism for the baryon asymmetry of the Universe.