Probing muon anomaly and lepton flavor violation with scalar leptoquarks in the 331LHN model

Abstract

We extend the $SU(3)_C \times SU(3)_L \times U(1)_X$ model with neutral leptons (331LHN) by introducing scalar leptoquarks. We determine the particle content of the leptoquark multiplets and their Yukawa interactions with fermions. We find that a singlet leptoquark can fully account for the $4.2\sigma$ discrepancy in the muon anomalous magnetic moment $\Delta a_\mu^{2021}$. The corresponding leptoquark mass is constrained to be $m_S \gtrsim 1.8$~TeV, consistent with current LHC bounds. We further consider the updated $\Delta a_\mu^{2025}$ based on recent lattice QCD results, which strengthen the lower bound to $m_S \gtrsim 6$~TeV. Combining $\Delta a_\mu$ with low-energy leptonic observables, including charged lepton flavor violation and the $\mu$--$e$ conversion rate, we constrain the viable parameter space. The allowed leptoquark Yukawa couplings exhibit a normal hierarchical pattern under all constraints. We also investigate the collider phenomenology of the singlet leptoquark, showing that its QCD-driven pair production leads to suppressed signal rates at the LHC for multi-TeV masses, while future hadron colliders can significantly extend the discovery reach.