In this paper, we calculate the $B_cto J/psi$ helicity form factors (HFFs) up to twist-4 accuracy by using the light-cone sum rules approach. After extrapolating those HFFs to the physically allowable $q^2$ region, we investigate the $B^+_c$-meson tw
o-body decays and semi-leptonic decays $B_c^+ to J/psi+(P, V, ell^+ u_ell)$, where $P$ and $V$ stand for a light pseudo-scalar meson and a vector meson, respectively. The branching fractions can be derived by using the CKM matrix element and the $B_c$ lifetime from the Particle Data Group, and we obtain ${cal B}(B_c^+ to J/psi pi^+)=(0.132^{+0.002}_{-0.002})%$, ${cal B}(B_c^+ to J/psi K^+)=(0.010^{+0.000}_{-0.000})%$, ${cal B}(B_c^+ to J/psi rho^+) =(0.755^{+0.030}_{-0.034})%$, ${cal B}(B_c^+ to J/psi K^{ast +})=(0.043^{+0.001}_{-0.001})%$, ${cal B}(B_c^+ to J/psi mu^+ u_mu)=(2.808^{+0.547}_{-0.704})%$ and ${cal B}(B_c^+ to J/psi tau^+ u_tau)=(0.563^{+0.137}_{-0.178})%$. We then obtain ${cal R}_{pi^+/mu^+ u_mu} = 0.047^{+ 0.009}_{-0.012}$ and ${cal R}_{K^+ / pi^+} = 0.075^{+0.005}_{-0.005}$, which agree with the LHCb measured value within $1sigma$-error. We also obtain ${cal R}_{J/psi}=0.200^{+ 0.062}_{-0.081}$, which like other theoretical predictions, are consistent with the LHCb measured value within $2sigma$-error.
We make a detailed study on the typical production channel of double charmoniums, $e^+e^-to J/psi+eta_c$, at the center-of-mass collision energy $sqrt{s}=10.58$ GeV. The key component of the process is the form factor $F_{rm VP}(q^2)$, which has been
calculated within the QCD light-cone sum rules (LCSR). To improve the accuracy of the derived LCSR, we keep the $J/psi$ light-cone distribution amplitude up to twist-4 accuracy. Total cross sections for $e^+e^-to J/psi+eta_c$ at three typical factorization scales are $sigma|_{mu_s} = 22.53^{+3.46}_{-3.49}~{rm fb}$, $sigma|_{mu_k} = 21.98^{+3.35}_{-3.38}~{rm fb}$ and $sigma|_{mu_0} = 21.74^{+3.29}_{-3.33}~{rm fb}$, respectively. The factorization scale dependence is small, and those predictions are consistent with the BABAR and Belle measurements within errors.
In this paper, we make a detailed study about the $Dto V$ 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 $|V_{cq}|$-independent decay widths of semileptonic decay $Dto Vell^+ u_ell$. 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 $P_{rm L,T}^ell$ ($F_{rm L,T}^ell$), the forward-backward asymmetry ${cal A}_{rm FB}^ell$, and the lepton-side convexity parameters ${cal C}_{rm F}^ell$. 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.
Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the central interests in spintronics applications. Here we report a giant Gilbert damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a maximum-minimum damping rat
io of 400 %, determined by broadband spin-torque as well as inductive ferromagnetic resonance. We conclude that the origin of this damping anisotropy is the variation of the spin orbit coupling for different magnetization orientations in the cubic lattice, which is further corroborate from the magnitude of the anisotropic magnetoresistance in Co$_{50}$Fe$_{50}$.
Taking advantage of an extended Lugiato--Lefever equation with third-order dispersion, we numerically show that dark cavity solitons formed in normal dispersion of microresonators are capable of emitting dispersive waves in both normal and anomalous
dispersion regions, resembling the behavior of the commonly encountered bright cavity solitons. The generated dispersive waves can be accurately predicted by the dissipative radiation theory. In addition, we demonstrate the stability enhancement of Kerr frequency combs in normal dispersion regime in case the dispersive wave is emitted by dark solitons in presence of third-order dispersion.
