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

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 ($pp\to {\ell }^{+}{\ell }^{-}$) 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.

Comments: 43 pages + references, expanded $h\to \mu \mu$ discussion, added references, matches published version