Study of B_s → $D_{s}^{*} \tau \bar {\nu }$ Decay in the Aligned Two-Higgs-Doublet Model and Vector Leptoquark Model

Abstract

In this paper, with the form factors calculated in the relativistic quark model, B_s → $D_{s}^{*} \tau \bar {\nu }$ decay is studied in the aligned two-Higgs-doublet model (A2HDM) and vector leptoquark model. Using the parameter spaces obtained from flavor constraints, we calculate the branching ratio ${\mathscr{B}}(B_{s}\to D_{s}^{*} \tau \bar {\nu })$ and the integrated ratio $R_{D_{s}^{*}}$ within the standard model (SM), A2HDM and vector leptoquark model. Moreover, we also show the effects of A2HDM and vector leptoquark model on some observables, such as the differential branching ratio $\frac {d{\mathscr{B}}}{dq^{2}}$, the differential ratio $R_{D_{s}^{*}}(q^{2})$, the lepton-side forward-backward asymmetry A_FB(q²), the longitudinal polarization fractions $P_{L}^{\tau }(q^{2})$ and $P_{L}^{D_{s}^{*}}(q^{2})$. We find, (i) the SM results of ${\mathscr{B}}(B_{s}\to D_{s}^{*} \tau \bar {\nu })$ can be enhanced about 2σ by the contributions of both A2HDM and vector leptoquark model, which can enhance the SM results of $R_{D_{s}^{*}}$ by about 5σ and 7σ, respectively. (ii)all of these considered observables are sensitive to the A2HDM effects. However, the vector leptoquark model effects are trivial for A_FB(q²), $P_{L}^{\tau }(q^{2})$ and $P_{L}^{D_{s}^{*}}(q^{2})$ with the exception of other considered observables.