Branching fractions and polarizations of $D\to V(\omega ,\rho ,K^{\ast })\mathrm{\ell }{\nu }_{\mathrm{\ell }}$ within QCD LCSR

In this paper, we make a detailed study about the $D\to V$ helicity form factors (HFFs) within the framework of QCD light-cone sum rule (LCSR) up to twist-4 accuracy. After extrapolating the LCSR predictions of HFFs to the whole physical $q^2$-region, we get the longitudinal, transverse and total $\mathrm{\mid }{V}_{cq}\mathrm{\mid }$-independent decay widths of semileptonic decay $D\to V\ell^+\nu_\ell$. Meanwhile, the branching fractions of these decays are also obtained by using the $D^0(D^{+})$-meson lifetime, which agree well with the BES-III results within errors. As a further step, we also investigate the differential and mean predictions for charged lepton (vector meson) polarization in the final state $P_{\mathrm{L},\mathrm{T}}^{\mathrm{\ell }}$ ($F_{\mathrm{L},\mathrm{T}}^{\mathrm{\ell }}$), the forward-backward asymmetry ${\mathcal{A}}_{\mathrm{F}\mathrm{B}}^{\mathrm{\ell }}$, and the lepton-side convexity parameters ${\mathcal{C}}_{\mathrm{F}}^{\mathrm{\ell }}$. Our predictions are consistent with Covariant Confining Quark Model results within the errors. Thus, we think the LCSR approach for HFFs is applicable for dealing with the $D$-meson semileptonic decays.