Electromagnetic leptogenesis -- an EFT-consistent analysis via Wilson coefficients. Part III. Probing light-neutrino masses and low-energy observables

TL;DR

The paper investigates electromagnetic leptogenesis within an EFT framework by tracing the dipole operator from a UV completion to low energies and testing its compatibility with light-neutrino masses and precision dipole observables.The analysis shows that the radiative Majorana neutrino masses generated by double insertions of the dipole operator are generically negligible in the BAU-friendly region, requiring additional UV contributions to the Weinberg operator to account for observed neutrino masses.The charged-lepton dipole operator in LEFT, $\mathcal{O}_{e\gamma}$, receives both one-loop mixing and two-loop Barr--Zee-type contributions, but the resulting low-energy signals for BR$(\mu\to e\gamma)$, the electron EDM, and $(g-2)_\mu$ remain several orders of magnitude below current experimental sensitivities within the BAU-compatible parameter space.Overall, the resonant EMLG scenario at the electroweak scale is robust against present constraints from light-neutrino masses and low-energy dipole probes, offering a coherent EFT picture that links baryogenesis to neutrino physics while predicting tiny low-energy imprints.

Abstract

In this third part of our EFT-consistent analysis of electromagnetic leptogenesis, we confront the dipole operator that sources the baryon asymmetry with constraints from light-neutrino masses and low-energy observables. Starting from the UV completion and one-loop-matched Wilson coefficient $C_{NB}$ of the gauge-invariant operator $O_{NB}=(\bar{L}σ^{μν}P_RN)\tilde{H}B_{μν}$, we compute the radiatively induced Weinberg operator $O_5$ and derive the light Majorana mass matrix generated by a double insertion of $O_{NB}$. For the benchmarks that realise successful resonant electromagnetic leptogenesis at the electroweak scale, these contributions yield neutrino masses far below the scale implied by neutrino oscillation data, so that the observed neutrino masses must originate from additional interactions such as one of the seesaw mechanisms, and only in extreme corners of parameter space do they saturate the cosmological bound on $\sum m_ν$. We also show that no additional Dirac neutrino mass is generated at one loop by the dipole operator alone. Furthermore, we derive the charged-lepton dipole operator $O_{eγ}$ in LEFT, accounting for one-loop operator mixing in the symmetric phase and two-loop Barr-Zee-type graphs in the broken phase, and evolve its Wilson coefficient $C_{eγ}$ down to the muon and electron mass scales using QED renormalisation-group equations. The resulting analytic upper bounds on $\mathrm{BR}(μ\to eγ)$, the electron EDM, and $(g-2)_μ$ lie many orders of magnitude below current experimental sensitivities throughout the BAU-compatible region. Electromagnetic leptogenesis in this EFT framework is therefore robust against present constraints from light-neutrino masses and low-energy dipole probes.

Figures (6)

• Figure 1: Contribution of the electromagnetic dipole operator to the Majorana mass of light-neutrinos.
• Figure 2: Contribution of the electromagnetic dipole operator to the Dirac mass $m_D$.
• Figure 3: One-loop operator mixing in the electroweak-symmetric phase.
• Figure 4: Two-loop Barr--Zee--type graphs in the broken phase.
• Figure 5: Comparison between the theoretical lines for the low-energy observables at the standard parameter choice (solid lines) and at the extreme benchmark (dashed lines), and the corresponding experimental bounds, where the region above each black dashed line is excluded. The theoretical lines are computed within the effective field theory derived from our UV model, and the experimental constraints are shown as rectangles with the same colour as their corresponding lines. (continued below)