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Register a new userLeft-Right SU(4) Vector Leptoquark Model for Flavor Anomalies
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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.
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In the recently proposed dark left-right gauge model of particle interactions, the left-handed fermion doublet $( u,e)_L$ is connected to its right-handed counterpart $(n,e)_R$ through a scalar bidoublet, but $ u_L$ couples to $n_R$ only through $phi_1^0$ which has no vacuum expectation value. The usual R parity, i.e. $R = (-)^{3B+L+2j}$, can be defined for this nonsupersymmetric model so that both $n$ and $Phi_1$ are odd together with $W_R^pm$. The lightest $n$ is thus a viable dark-matter candidate (scotino). Here we explore the phenomenology associated with the $SU(2)_R$ gauge group of this model, which allows it to appear at the TeV energy scale. The exciting possibility of $Z to 8$ charged leptons is discussed.
We argue that dark matter can automatically arise from a gauge theory that possesses a non-minimal left-right gauge symmetry, SU(3)_C otimes SU(M)_L otimes SU(N)_R otimes U(1)_X, for (M,N) = (2,3), (3,2), (3,3), cdots, and (5,5).
We reconsider a model introducing a scalar leptoquark $phi sim (mathbf{3}, mathbf{1}, -1/3)$ to explain recent deviations from the standard model in semileptonic $B$ decays. The leptoquark can accommodate the persistent tension in the decays $bar{B}rightarrow D^{(*)}tau bar{ u}$ as long as its mass is lower than approximately $10 text{ TeV}$, and we show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. Agreement with the measured $bar{B}rightarrow D^{(*)}tau bar{ u}$ rates is mildly compromised for parameter choices addressing the tensions in $b to s mu mu$, where the model can significantly reduce the discrepancies in angular observables, branching ratios and the lepton-flavor-universality observables $R_K$ and $R_{K^*}$. The leptoquark can also reconcile the predicted and measured value of the anomalous magnetic moment of the muon and appears naturally in models of radiative neutrino mass derived from lepton-number violating effective operators. As a representative example, we incorporate the particle into an existing two-loop neutrino mass scenario derived from a dimension-nine operator. In this specific model, the structure of the neutrino mass matrix provides enough freedom to explain the small masses of the neutrinos in the region of parameter space dictated by agreement with the anomalies in $bar{B}rightarrow D^{(*)}tau bar{ u}$, but not the $b to s$ transition. This is achieved without excessive fine-tuning in the parameters important for neutrino mass.
Motivated by the ongoing searches for new physics at the LHC, we explore the low energy consequences of a D-brane inspired $ SU(4)_Ctimes SU(2)_L times SU(2)_R$ (4-2-2) model. The Higgs sector consists of an $SU(4)$ adjoint, a pair $H+bar H$ in $(4,1,2)+(bar 4,1,2)$, and a bidoublet field in $h(1,2,2)$. With the $SU(4)$ adjoint the symmetry breaks to a left-right symmetric $SU(3)_Ctimes U(1)_{B-L} times SU(2)_L times SU(2)_R$ model. A missing partner mechanism protects the $SU(2)_R$ Higgs doublets in $H,bar H$, which subsequently break the symmetry to the Standard Model at a few TeV scale. An inverse seesaw mechanism generates masses for the observed neutrinos and also yields a sterile neutrino which can play the r^ole of dark matter if its mass lies in the keV range. Other phenomenological implications including proton decay are briefly discussed.
We show that a single vector leptoquark can explain both the muon $g-2$ anomaly recently measured by the Muon g-2 experiment at Fermilab, and the various $B$ decay anomalies, including the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies which have been recently reported by the LHCb experiment. In order to provide sizeable positive new physics contributions to the muon $g-2$, we assume that the vector leptoquark particle couples to both left-handed and right-handed fermions with equal strength. Our model is found to satisfy the experimental constraints from the large hadron collider.
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