Unified SU(4) theory for the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies

TL;DR

This paper introduces a unified SU(4) Pati-Salam model that explains anomalies in B-meson decays through leptoquarks, predicts a sterile neutrino, and remains consistent with current experiments, with future tests planned.

Contribution

The paper presents a novel chiral Pati-Salam theory that unifies quarks and leptons and explains B-meson decay anomalies via scalar and gauge leptoquarks, predicting a testable sterile neutrino.

Findings

Explains $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies with leptoquarks.

Predicts a sub-GeV sterile neutrino accessible in future experiments.

Model is consistent with current experimental constraints.

Abstract

We propose a chiral Pati-Salam theory based on the gauge group $SU(4)_C\times SU(2)_L\times SU(2)_R$. The left-handed quarks and leptons are unified into a fundamental representation of $SU(4)_C$, while right-handed quarks and leptons have a separate treatment. The deviations measured in the rare semi-leptonic decays $B\to D^{(*)} \tau\bar\nu$ are explained by a scalar leptoquark which couples to right-handed fields and is contained in the $SU(4)_C\times SU(2)_R$ breaking scalar multiplet. The measured deviation of lepton flavor universality in the rare decays $\bar B\to \bar K^{(*)}\ell^+\ell^-$, $\ell=\mu,e$ is explained via the $SU(4)_C$ leptoquark gauge boson. The model predicts a new sub-GeV scale sterile neutrino which participates in the anomaly and can be searched for in upcoming neutrino experiments. The theory satisfies the current most sensitive experimental constraints and its allowable parameter regions will be probed as more precise measurements from the LHCb and Belle II experiments become available.