Constraining the new contributions to electron $g-2$ in a radiative neutrino mass model

TL;DR

The paper analyzes a radiative neutrino mass model with two TeV-scale scalar leptoquarks $S(3,1,-1/3)$ and $R(3,2,1/6)$, using decoupled electron and muon textures to separate the leptonic g-2 enhancements from different up-type quarks. It demonstrates that fitting neutrino oscillation data requires both one- and two-loop contributions to the neutrino mass matrix, which, together with oscillation constraints, severely restricts the parameter space and yields only small new-physics contributions to $\delta a_\mu$, while allowing the electron g-2 discrepancy to be addressed at the $2\sigma$ level in inverted mass ordering. The framework also predicts lepton-flavor-violating tau decays near present experimental limits and imposes strong correlations with electroweak and high-$p_T$ precision observables, offering multiple avenues for testing via future neutrino, collider, and LFV experiments.

Abstract

We examine electron and muon anomalous magnetic dipole moments within a radiative neutrino mass model featuring TeV-scale scalar leptoquarks $S(3,1,-1/3)$ and $R(3,2,1/6)$. We utilize textures with decoupling electron and muon sectors, so that both electron and muon anomalous magnetic dipole moments could receive internal chiral enhancements from different heavy up-type quarks while in the same time evading the stringent $μ\to eγ$ constraint. A successful fit to neutrino oscillation data requires the simultaneous presence of one- and two-loop neutrino mass contributions. This severely constrains the parameter space of the model, which results in a negligible new physics correction to the muon $g-2$. The electron $g-2$ discrepancy implied by the rubidium experiment, on the other hand, can be resolved within $2σ$ uncertainty provided that neutrino mass ordering is inverted. Lepton-flavor-violating tau decay rates, such as $τ\to eγ$ and $τ\to 3e$, are predicted to be within the sensitivities of next-generation experiments.

Figures (4)

• Figure 1: One- and two-loop diagrams leading to neutrino mass generation.
• Figure 2: Comparison between numerical (solid) and approximated (dashed) values of the two-loop integral in the case of light quarks (left) and top quark (right) inside the loop.
• Figure 3: Plots of magnitudes and arguments of neutrino mass parameters in NO and IO. Since the solutions for $a$ ($b$) are complementary to those of $w$ ($v$), only the allowed regions of $w$ and $v$ are shown in the upper panel. The relative strengths between $(a,w)$ and $(b,v)$ are shown in the lower panel.
• Figure 4: The allowed region presented in $|\lambda^u_{21}|$ vs $|\lambda^R_{21}|$ plane for TX 1 (left) and in $|\lambda^u_{31}|$ vs $|\lambda^R_{31}|$ plane for TX 2 (right). The darker (lighter) shaded area corresponds to one- (two-) sigma allowed region of $a_e^\text{exp}-a_e^\text{Rb}$, while the area bordered by the dashed lines correspond to two-sigma allowed region of $|a_e^\text{exp}-a_e^\text{Cs}|$.