Electromagnetic leptogenesis — an EFT-consistent analysis via Wilson coefficients. Part II. Low-scale, resonant regime

A bstract We study electromagnetic leptogenesis (EMLG) in the low-scale, resonant regime in the specific minimal renormalisable UV completion that generates the gauge-invariant dipole operator $$ {\mathcal{O}}_{NB} $$ O NB = $$ \left(\overline{L}{\sigma}^{\mu \nu}N\right)\overset{\sim }{H}{B}_{\mu \nu} $$ L ¯ σ μν N H ~ B μν . Starting from this UV Lagrangian, we perform a one-loop matching to obtain the Wilson coefficient C NB , implement the Pilaftsis-Underwood resummation of self-energy effects in the CP asymmetries for a quasi-degenerate right-handed-neutrino pair, and evolve a flavour-covariant transport system across the broken-phase electroweak window. At the level of the dipole sector alone, the quasi-degenerate condition M m – M i ≃ Γ m /2 ( m ≠ i ) yields the expected Breit-Wigner enhancement of the CP-odd source. In the minimal completion under study, however, neutrino Yukawa interactions are unavoidably present and must be incorporated consistently through their contributions to the physical total widths and the associated dilution and washout effects. Once this UV-implied width and washout structure is included, the dipole-driven baryon asymmetry is strongly suppressed and remains far below the observed value. Our results therefore establish a UV-induced obstruction to low-scale resonant EMLG within this minimal completion, complementing the gauge-imposed suppression found in Part I, and motivate alternative UV constructions in which the dipole operator is generated without inducing sizable $$ \overline{L}\overset{\sim }{H}N $$ L ¯ H ~ N interactions for the leptogenesis-relevant sterile sector.