In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic \( {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } \) decay. This decay is of interest in light of the R(D^(*)) puzzle in the semileptonic \( \overline{B}\to {D}^{\left(\ast \right)}\tau {\overline{\nu}}_{\tau } \) decays. In this work we add tensor operators to extend our previous results and consider both model-independent new physics (NP) and specific classes of models proposed to address the R(D^(*)) puzzle. We show that a measurement of \( R\left({\Lambda}_c\right)=\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau}\right]/\mathrm{\mathcal{B}}\left[{\Lambda}_b\to {\Lambda}_c\ell {\overline{\nu}}_{\ell}\right] \) can strongly constrain the NP parameters of models discussed for the R(D^(*)) puzzle. We use form factors from lattice QCD to calculate all \( {\Lambda}_b\to {\Lambda}_c\tau {\overline{\nu}}_{\tau } \) observables. The Λ_b → Λ_c tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.

We propose a scheme, based on $\mathrm{\Delta }(27)$ flavor symmetry and supplemented by other discrete symmetries and the inverse seesaw mechanism, where both the light neutrino masses and the deviation from tribimaximal mixing matrix can be linked to the source of lepton number violation. The hierarchies of the charged leptons are explained. We find that the quark masses including their hierarchies and the mixing can also be constructed in a similar way.

For a number of years, there has been a certain inconsistency among the measurements of the branching ratios and CP asymmetries of the four B -> pi K decays (B+ -> pi(+) K-0, B+ -> pi K-0(+), B-d(0) -> pi K--(+), B-d(0) -> pi K-0(0)). In this paper, we re- examine this B -> pi K puzzle. We find that the key unknown parameter is vertical bar C'/T'vertical bar, the ratio of color-suppressed and color-allowed tree amplitudes. If this ratio is large, vertical bar C'/T'vertical bar = 0.5, the SM can explain the data. But if it is small, vertical bar C'/T'vertical bar = 0.2, the SM cannot explain the B -> pi K puzzle new physics (NP) is needed. The two types of NP that can contribute to B -> pi K at tree level are Z' bosons and diquarks. Z' models can explain the puzzle if the Z' couples to right-handed u (u) over bar and/or d (d) over bar, with g(R)(dd)/g(R)(uu). Interestingly, half of the many Z' models proposed to explain the present anomalies in b -> s mu(+) mu(-) decays have the required Z' couplings to u (u) over bar and/ or d (d) over bar. Such models could potentially explain both the b -> s mu(+) mu(-) anomalies and the B -> pi K puzzle. The addition of a color sextet diquark that couples to u d can also explain the puzzle.

In this work we study the effects of new-physics (NP) operators with different Lorentz structures on the inclusive $B\to X_c\tau \overline{\nu }$ decay and make predictions for the ratio of total decay rates $R(X_c)=\frac{\mathrm{\Gamma }(B\to X_c\tau {\overline{\nu }}_{\tau })}{\mathrm{\Gamma }(B\to X_c\ell {\overline{\nu }}_{\ell })}$ with $\ell =e$, $\mu$, the differential decay rates, $\frac{d\mathrm{\Gamma }}{d{q}^2}$ and $\frac{d\mathrm{\Gamma }}{d{E}_{\tau }}$, forward-backward asymmetry $A_{\mathrm{F}\mathrm{B}}$ and the ratio of the differential decay rates $B(q^2)=\frac{d\mathrm{\Gamma }(B\to X_c\tau {\overline{\nu }}_{\tau })/d{q}^2}{d\mathrm{\Gamma }(B\to X_c\ell {\overline{\nu }}_{\ell })/d{q}^2}$. In addition, we introduce some leptoquark models as explicit models of the NP operators and study their effects on the inclusive decay. We consider $\mathcal{O}({\alpha }_s)$ radiative and $1/m_b$ nonperturbative corrections to the Standard Model (SM) decay rate and ignore their small effects in the NP contributions.

We study flavor changing neutral current decays of B and K mesons in the dark U(1)_D model, with the dark photon/dark Z mass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions of B → K^(∗)ℓ⁺ℓ⁻, with ℓ = μ, e, and B_s→ ϕμ⁺μ⁻, the allowed parameter space is ruled out by measurements of atomic parity violation, K⁺→ μ⁺ + invisible decay, and $$ {B}_s-{\overline{B}}_s $$B s − B ¯ s mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisible Z_D decay, (2) a direct vector coupling of Z_D to muons, and (3) a direct coupling of Z_D to both muons and electrons, with the electron coupling fine-tuned to cancel the Z_D coupling to electrons via mixing. We find that only the latter case survives all constraints.