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

Abstract We analyse electromagnetic leptogenesis within the framework of an effective field theory, where the dynamics is governed by the gauge-invariant dipole operator $${\mathcal{O}}_{NB}=\left(\overline{L}{\sigma }^{\mu \nu }N\right)\widetilde{H}{B}_{\mu \nu }$$ . The Wilson coefficient C NB is matched at one loop and evolved to the electroweak scale via renormalisation-group (RG) running. After electroweak symmetry breaking, we compute flavour-dependent decay widths and CP asymmetries for the two-body modes N → νγ and N → νZ , and solve the fully flavoured Boltzmann equations. In the N 1 -dominated regime, the freeze-out baryon asymmetry is $${Y}_{B}^{\text{FO}}\lesssim {1}{0}^{-{17}}$$ , far below the observed value $${Y}_{B}^{\text{obs}}\simeq 8.7\times {10}^{-11}$$ . The suppression is structural: gauge invariance forces a Higgs insertion; therefore the dipole coupling scales as $$\mu \propto v/{M}_{\psi}^{2}$$ , while the matched Wilson coefficient C NB is loop-generated and further suppressed by RG running. We note that in the quasi-degenerate limit the self-energy resonance can be operative and suggest a plausible path to $${Y}_{B}^{\text{obs}}$$ .