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.
Highlights
The standard model (SM) of particle physics with the inclusion of neutrino masses describes nature with unprecedented precision and has so far withstood all experimental tests
As the explanations for the RKðÃÞ and RDðÃÞ anomalies are mostly independent, we first discuss the explanation of RKðÃÞ, which sets the scale of the SUð4ÞC × SUð2ÞL × SUð2ÞR symmetry breaking
We have proposed a chiral Pati-Salam theory with gauge group SUð4ÞC × SUð2ÞL × SUð2ÞR which is capable of explaining the RDðÃÞ anomalies with new scalar leptoquarks and the RKà anomalies via SUð4Þ gauge boson leptoquarks
Summary
The standard model (SM) of particle physics with the inclusion of neutrino masses describes nature with unprecedented precision and has so far withstood all experimental tests. We consider a simple extension of the model with a larger gauge group SUð4ÞC× SUð2ÞL × SUð2ÞR, which further unifies the right-handed matter fields This allows explanation of the RDðÃÞ anomalies with a new scalar leptoquark χ ∼ ð3; 1; −2=3Þ,3 which is part of the scalar breaking of the Pati-Salam gauge group to the SM gauge group. We propose a model based on the gauge group SUð4ÞC × SUð2ÞL × SUð2ÞR and assign the particle content such that the SUð4Þ leptoquark gauge boson couples to the quarks and leptons in a chiral fashion. This naturally avoids strong constraints from charged lepton-flavor-violating leptonic neutral meson decays such as KL → eÆμ∓ and B → eÆμ∓.
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