Abstract
Building on our recent proposal to explain the experimental hints of new physics in $B$ meson decays within the framework of Pati-Salam quark-lepton unification, through the interactions of the $(3,1)_{2/3}$ vector leptoquark, we construct a realistic model of this type based on the gauge group ${\rm SU}(4)_L \times {\rm SU}(4)_R \times {\rm SU}(2)_L \times {\rm U}(1)'$ and consistent with all experimental constraints. The key feature of the model is that ${\rm SU}(4)_R$ is broken at a high scale, which suppresses right-handed lepton flavor changing currents at the low scale and evades the stringent bounds from searches for lepton flavor violation. The mass of the leptoquark can be as low as $10 \ {\rm TeV}$ without the need to introduce mixing of quarks or leptons with new vector-like fermions. We provide a comprehensive list of model-independent bounds from low energy processes on the couplings in the effective Hamiltonian that arises from generic leptoquark interactions, and then apply these to the model presented here. We discuss various meson decay channels that can be used to probe the model and we investigate the prospects for discovering the new gauge boson at future colliders.
Highlights
The Standard Model (SM) provides a remarkably successful description of nature at the elementary particle level and, so far, there are only a handful of experimental indications of deviations from its predictions
The first attempt to construct a vector leptoquark model for the RKðÃÞ anomalies was made in [6], where we proposed that the vector leptoquark ð3; 1Þ2=3 explaining the anomalies might be the gauge boson of a theory with Pati-Salam unification
We have constructed a new model to account for the recently observed anomalies in B meson decays set within the framework of Pati-Salam unification
Summary
The Standard Model (SM) provides a remarkably successful description of nature at the elementary particle level and, so far, there are only a handful of experimental indications of deviations from its predictions. Perhaps the most significant direct hint of physics beyond the SM are the recently observed anomalies in B meson decays [1,2], which suggest that lepton universality might be violated Assuming that those anomalies are not a result of experimental systematics, they are best accounted for by the vector leptoquark ð3; 1Þ2=3 or ð3; 3Þ2=3 [3,4,5]. Several other models for the flavor anomalies based on Pati-Salam unification have been proposed, some appearing almost immediately after our initial work [13,14,15,16,17,18,19] Those models overcome the experimental constraints by mixing all or a subset of SM quarks and leptons with new vectorlike fermions. For B decays we use the most recent lattice results for the form factors [28], which weaken the bounds considerably compared to assuming the nonphysical values fþ 1⁄4f0 1⁄41 adopted previously in the literature
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