A quark-lepton unified Pati-Salam model with Z2 symmetry realizes a leptoquark gauge boson as light as 4.3 TeV, compatible with LHC and flavor constraints, and predicts testable lepton flavor violation plus new vector-like quarks.
$B$ Meson Anomalies in a Pati-Salam Model within the Randall-Sundrum Background
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abstract
Lepton number as a fourth color is the intriguing theoretical idea of the famous Pati-Salam (PS) model. While in conventional PS models, the symmetry breaking scale and the mass of the resulting vector leptoquark are stringently constrained by $K_L\to\mu e$ and $K\to\pi\mu e$, the scale can be lowered to a few TeV by adding vector-like fermions. Furthermore, in this case, the intriguing hints for lepton flavour universality violation in $b\to s\mu^+\mu^-$ and $b\to c\tau\nu$ processes can be addressed. Such a setup is naturally achieved by implementing the PS gauge group in the five-dimensional Randall-Sundrum background. The PS symmetry is broken by boundary conditions on the fifth dimension and the resulting massive vector leptoquark automatically has the same mass scale as the vector-like fermions and all other resonances. We consider the phenomenology of this model in the context of the hints for lepton flavour universality violation in semileptonic $B$ decays. Assuming flavour alignment in the down sector we find that in $b\to s\ell^+\ell^-$ transitions the observed deviations from the SM predictions (including $R(K)$ and $R(K^*)$) can be explained with natural values for the free parameters of the model. Even though we find sizable effects in $R(D)$, $R(D^*)$ and $R(J/\Psi)$ one cannot account for the current central values in the constrained setup of our minimal model due to the stringent constraints from $D-\bar D$ mixing and $\tau\to 3\mu$.
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Including resonant contributions from LHCb muon data enhances standard model predictions for B to K(*) tau tau decays and makes short-distance new physics comparable to or larger than resonant effects over the full q2 range.
Angular observables in B→D(*)ℓν decays can distinguish Lorentz structures of new physics contributions fitted to measured R(D(*)) ratios, even when those ratios agree with the Standard Model.
Predictions for Br(Λ_b → Λ^{(*)} ν ν̄) are 2.07 times the SM value with new physics scale constrained to 2.04–11.76 TeV at 1σ, plus a sum rule linking baryonic and mesonic modes.
A tauphilic leptoquark model with S1 explaining R(D(*)), ~R2 fitting B to K nu nu via right-handed coefficients, and S3 satisfying Delta m_Bs via mixing predicts subdominant negative C_VL, dominant positive C_SL, C9^LQ approx +1, and masses below 3 TeV.
citing papers explorer
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TeV Scale Quark-Lepton Unification
A quark-lepton unified Pati-Salam model with Z2 symmetry realizes a leptoquark gauge boson as light as 4.3 TeV, compatible with LHC and flavor constraints, and predicts testable lepton flavor violation plus new vector-like quarks.
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Impact of Hadronic Resonances on $B\to K^{(*)}\tau^+\tau^-$ decays
Including resonant contributions from LHCb muon data enhances standard model predictions for B to K(*) tau tau decays and makes short-distance new physics comparable to or larger than resonant effects over the full q2 range.
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Lepton Flavor Universality tests through angular observables of $\overline{B}\to D^{(\ast)}\ell\overline{\nu}$ decay modes
Angular observables in B→D(*)ℓν decays can distinguish Lorentz structures of new physics contributions fitted to measured R(D(*)) ratios, even when those ratios agree with the Standard Model.
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$\Lambda_b\to\Lambda^{(*)}\nu{\bar\nu}$ and $b\to s$ $B$ decays
Predictions for Br(Λ_b → Λ^{(*)} ν ν̄) are 2.07 times the SM value with new physics scale constrained to 2.04–11.76 TeV at 1σ, plus a sum rule linking baryonic and mesonic modes.
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$B$ anomalies and the tauphilic leptoquark model
A tauphilic leptoquark model with S1 explaining R(D(*)), ~R2 fitting B to K nu nu via right-handed coefficients, and S3 satisfying Delta m_Bs via mixing predicts subdominant negative C_VL, dominant positive C_SL, C9^LQ approx +1, and masses below 3 TeV.