Unified Framework for $B$-Anomalies, Muon $g-2$, and Neutrino Masses

TL;DR

This paper proposes a unified model explaining neutrino masses, B-meson decay anomalies, and muon g-2, using TeV-scale leptoquarks and Higgs quadruplets, with testable predictions at future colliders.

Contribution

The paper introduces a novel radiative neutrino mass model that simultaneously addresses multiple anomalies and predicts new collider signatures.

Findings

Neutrino masses fit with flavor constraints and anomalies within 1 sigma.

Flavor-dependent limits on leptoquark Yukawa couplings range from 0.15 to 0.36.

Predicted Higgs decay modifications at 2-6% level testable at future colliders.

Abstract

We present a model of radiative neutrino masses which also resolves anomalies reported in $B$-meson decays, $R_{D^{(\star)}}$ and $R_{K^{(\star)}}$, as well as in muon $g-2$ measurement, $\Delta a_\mu$. Neutrino masses arise in the model through loop diagrams involving TeV-scale leptoquark (LQ) scalars $R_2$ and $S_3$. Fits to neutrino oscillation parameters are obtained satisfying all flavor constraints which also explain the anomalies in $R_{D^{(\star)}}$, $R_{K^{(\star)}}$ and $\Delta a_\mu$ within $1\, \sigma$. An isospin-3/2 Higgs quadruplet plays a crucial role in generating neutrino masses; we point out that the doubly-charged scalar contained therein can be produced in the decays of the $S_3$ LQ, which enhances its reach to 1.1 (6.2) TeV at $\sqrt s=14$ TeV high-luminosity LHC ($\sqrt s=100$ TeV FCC-hh). We also present flavor-dependent upper limits on the Yukawa couplings of the LQs to the first two family fermions, arising from non-resonant dilepton ($pp \rightarrow \ell^+ \ell^-$) processes mediated by $t$-channel LQ exchange, which for 1 TeV LQ mass, are found to be in the range $(0.15 - 0.36)$. These limits preclude any explanation of $R_{D^{(\star)}}$ through LQ-mediated $B$-meson decays involving $\nu_e$ or $\nu_\mu$ in the final state. We also find that the same Yukawa couplings responsible for the chirally-enhanced contribution to $\Delta a_\mu$ give rise to new contributions to the SM Higgs decays to muon and tau pairs, with the modifications to the corresponding branching ratios being at (2-6)% level, which could be tested at future hadron colliders, such as HL-LHC and FCC-hh.