Left-right SU(4) vector leptoquark model for flavor anomalies

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 $\mathrm{SU}(4{)}_L\times \mathrm{SU}(4{)}_R\times \mathrm{SU}(2{)}_L\times \mathrm{U}(1{)}^{\prime }$ and consistent with all experimental constraints. The key feature of the model is that $\mathrm{SU}(4{)}_R$ 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 TeV without the need to introduce mixing of quarks or leptons with new vectorlike 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.

Figure 1

Expected number of events in $250{\mathrm{fb}}^{-1}$ of data collected by a 100 TeV $pp$ collider for the SM background $pp\to jj{\mu }^{+}{\mu }^{-}$ (blue) and the leptoquark signal $pp\to X_{L}j{\mu }^{-}\to jj{\mu }^{+}{\mu }^{-}$ for masses $M_{X_L}=10,12,14\mathrm{TeV}$ (red, orange, gray) as a function of the invariant mass of the highest $p_T$ jet and ${\mu }^{+}$. The values of parameters discussed in Sec. 4 were used.