Search

In this paper, we study the $B^{0} \to J/\psi h_{1}$ decays for the first time by using perturbative QCD approach up to the presently known next-to-leading order accuracy. The vertex corrections present significant contribution to the amplitude. In the calculation, the mixing between two light axial-vector mesons $h_{1}(1170)$ and $h_{1}(1415)$ are also studied in detail. The observables including the branching ratios, polarization fractions and $CP$ asymmetries are predicted and discussed explicitly. It is found that the $B^{0} \to J/\psi h_{1}$ decays have relatively large branching fractions, which are generally at the order of ${\cal O}(10^{-6}\sim10^{-3})$, and thus are possible to be observed by the LHCb and Belle-II experiments in the near future. Moreover, they are very sensitive to the mixing angle $\theta$ and can be used to test the values of $\theta$. In addition, some ratios between the branching fractions of $B^{0} \to J/\psi h_{1}$ decays can provide much stronger constraints on $\theta$ due to their relatively small theoretical errors. The $B^{0} \to J/\psi h_{1}$ decays are generally dominated by the longitudinal polarization contributions, specifically, $f_{L}(B^{0} \to J/\psi h_{1})>80\%$, except for the case that $\theta\sim 35^\circ$ and $-55^\circ$. Unfortunately, the direct $CP$ asymmetries of $B^{0} \to J/\psi h_{1}$ decays are too small to be observed soon even if the effect of $\theta$ is considered. The future precise measurements on $B^{0} \to J/\psi h_{1}$ decays are expected for testing these theoretical findings and exploring the interesting nature of $h_{1}(1170)$ and $h_{1}(1415)$., Comment: 23 pages, 6 figures, 8 tables

In this paper, the nonfactorizable photonic corrections to the effective four-fermion vertex for the $\overline{B}$ ${\to}$ $D^{({\ast})}$ $+$ ${\ell}^{-}$ $+$ $\bar{\nu}_{\ell}$ decays are considered at the quark level within SM, where ${\ell}$ $=$ $e$, ${\mu}$ and ${\tau}$. It is found that the QED corrections are closely related with the mass of the charged lepton. The QED contributions will enhance branching ratios, which results in the slight reduction of ratios $R(D^{(\ast)})$ and the relationship $R(D^{(\ast)})_{e}$ $<$ $R(D^{(\ast)})_{\mu}$., Comment: 27pages

The recently discovered stellar system, Ursa Major III/UNIONS 1, may be the faintest and densest dwarf spheroidal satellite galaxy of the Milky Way. Owing to its close proximity and substantial dark matter (DM) component, Ursa Major III emerges as a highly promising target for DM indirect detection. It is known that electrons and positrons originating from DM annihilation can generate a broad radio spectrum through the processes of synchrotron radiation and inverse Compton scattering within galaxies. In this study, we investigate the potential of the Square Kilometre Array (SKA) in detecting radio signatures arising from DM annihilation in Ursa Major III over a 100 hour observation period. Our analysis indicates that the SKA has strong capabilities in detecting these signatures. For instance, the SKA sensitivity to the DM annihilation cross section is estimated to reach $\mathcal{O}(10^{-30})-\mathcal{O}(10^{-28})\; \rm cm^{3} s^{-1}$ in the DM mass range from several GeV to $\sim100$ GeV for the $e^+e^-$ and $\mu^+\mu^-$ annihilation channels. The precise results are significantly influenced by various astrophysical factors, such as the strength of magnetic field, the diffusion coefficient, and the DM density profile in the dwarf galaxy. We discuss the impact of the uncertainties associated with these factors, and find that the SKA sensitivities have the potential to surpass the current constraints, even when considering these uncertainties., Comment: 20 pages, 6 figures

In this work, we calculated the form factors of the weak decay process $\Lambda_b^0 \to \Lambda_c(2595)^+$, where the final charm baryon represents an excited state with spin-parity $\frac{1}{2}^-$. Utilizing the light-cone QCD sum rules approach, we incorporated the contributions of the lowest two charm baryon states: the ground state $\Lambda_c$ with $J^P=\frac{1}{2}^+$ and the excited state $\Lambda_c(2595)^+$ with $J^P=\frac{1}{2}^-$ in the hadronic representation of the $\Lambda_b \to \Lambda_c(2595)^+$ transition correlation function. This approach allows us to extract the form factors of the $\Lambda_b^0 \to \Lambda_c(2595)^+$ from $\Lambda_b^0 \to \Lambda_c^+$ transition. During the light-cone QCD sum rules procedure, we employed the light-cone distribution amplitudes (LCDAs) of the $\Lambda_b$ baryon. Furthermore, by combining these form factors with the helicity amplitudes of the bottom baryon transition matrix elements, we calculated the differential decay widths for the processes $\Lambda_b^0 \to \Lambda_c(2595)^+\ell^-\bar{\nu}_\ell$ and provided the optimal choice of the interpolating current for $\Lambda_c$ in this process. Additionally, within the lifetime of $\Lambda_b^0$, we obtained the absolute branching fractions for the semileptonic decays $\Lambda_b^0 \to \Lambda_c(2595)^+ \ell^- \bar{\nu}_\ell$. With the branching fractions of $\Lambda_b^0 \to \Lambda_c(2595)^+ \ell^- \bar{\nu}_\ell$ calculated in this work, we also determined the parameter $R(\Lambda_c(2595)^+)$ which tests the lepton flavor universality. This parameter is defined as the ratio of branching fractions $Br(\Lambda_b^0 \to \Lambda_c(2595)^+\tau^-\bar{\nu}_\tau)$ and $Br(\Lambda_b^0 \to \Lambda_c(2595)^+\mu^-\bar{\nu}_\mu)$. Our results provide a valuable theoretical test for these decay channels and offer insights into the LCDAs of bottom baryons, paving the way for further in-depth investigations., Comment: 21 pages, 8 figures and 5 tables

Based on the fitting results of the LHCb collaboration on the contributions of various intermediate resonances to the $B^{+}\to\pi^{+}\pi^{+}\pi^{-}$ decay, we make systematically calculate the branching fractions and localized $CP$ asymmetries of the quasi-two-body $B^{+}\to \pi^{+} \left( \rho(770), \omega(782), \rho(1450), f_{2}\left(1270\right)\to\right)\pi^{+}\pi^{-}$ decays within the perturbative QCD (PQCD) approach. Our theoretical predictions for the branching fractions agree well with the data within the errors. In order to further test the framework of the three-body $B$ decays in PQCD and the wave functions of $\pi\pi$ pair, we also calculate the branching fractions of the corresponding two-body $B^{+}\to\pi^{+}\rho(770)$, $B^{+}\to\pi^{+}\omega(782)$ and $B^{+}\to\pi^{+}f_{2}\left(1270\right)$ decays under the narrow-width-approximation, which are in consistence with the experimental data. The direct $CP$ asymmetries of $B^{+}\to\pi^{+}(\rho(770/1450)\to) \pi^{+}\pi^{-}$ decays are found to be very small because these decay modes are tree-dominated. However, due to the large penguin contributions from the chiral enhanced annihilation diagrams, $B^{+}\to\pi^{+} (f_{2}\left(1270\right)\to )\pi^{+}\pi^{-}$ decay has a large direct $CP$ asymmetry, which is also discovered by LHCb collaboration. A relatively large $CP$ asymmetry is also expected in the $B^+\to\pi^+ (\omega\to)\pi^+\pi^-$ decay occurring via $\rho-\omega$ mixing, which would be measured LHCb and Belle-II experiments in future., Comment: 17 pages, 5 figure

Kinematics restrict the ability of rare charm decays to explore the charged Lepton Flavor Violation processes mediated by the quark-level $c\to u \ell \tau$ transition. To fill the gap, we propose exploring new physics (NP) through the quasielastic scattering process $e^-p\to \tau^-\Lambda_c$ and the polarization of the $\tau$ lepton. As analyzing modes for the $\tau$ polarization, we consider the decays $\tau^-\to \pi^-\nu_{\tau}$, $\tau^-\to \rho^-\nu_{\tau}$, and $\tau^- \to \ell^-\bar{\nu}_{\ell}\nu_{\tau}$, and show that the $\tau$ polarization components can be extracted from analyzing the kinematics of the $\tau$ visible decay products. In the framework of a general low-energy effective Lagrangian, we then perform a detailed analysis of the polarization components in various aspects and scrutinize possible NP signals. With one upcoming experimental setup, we finally demonstrate promising event rate can be expected for the cascade process and, even in the worst-case scenario -- no signals is observed at all -- it can still provide a competitive potential for constraining the NP, compared with those from the high-$p_T$ dilepton invariant mass tails at high-energy colliders., Comment: 20 pages, 4 figures, 5 tables

Inspired by the brilliant prospects of the ongoing $B$ meson experiments, the hadronic charmless $B$ ${\to}$ $SS$ decays are studied by considering the next-to-leading (NLO) contributions with the QCD factorization approach, where $S$ denotes the scalar mesons $K_{0}^{\ast}(1430)$ and $a_{0}(1450)$. Branching ratios and $CP$ violating asymmetries are estimated with the updated values of hadronic parameters obtained from a covariant light-front quark model, for two scenarios where the scalar mesons are the $1^{3}P_{0}$ and $2^{3}P_{0}$ states. It is found that the NLO contributions are very important for the $B$ ${\to}$ $SS$ decays; For the $B$ ${\to}$ $a_{0}(1450)K_{0}^{\ast}(1430)$ and $B_{s}$ ${\to}$ $K_{0}^{\ast}(1430)\overline{K}_{0}^{\ast}(1430)$ decays, branching ratios can reach up to the order of ${\cal O}(10^{-5})$ by assuming that the scalar mesons are the $1P$ states, and should first be investigated in the future experiments.

Multi-task learning (MTL) aims to improve the generalization performance of multiple tasks by exploiting the shared factors among them. Various metrics (e.g., F-score, Area Under the ROC Curve) are used to evaluate the performances of MTL methods. Most existing MTL methods try to minimize either the misclassified errors for classification or the mean squared errors for regression. In this paper, we propose a method to directly optimize the evaluation metrics for a large family of MTL problems. The formulation of MTL that directly optimizes evaluation metrics is the combination of two parts: (1) a regularizer defined on the weight matrix over all tasks, in order to capture the relatedness of these tasks; (2) a sum of multiple structured hinge losses, each corresponding to a surrogate of some evaluation metric on one task. This formulation is challenging in optimization because both of its parts are non-smooth. To tackle this issue, we propose a novel optimization procedure based on the alternating direction scheme of multipliers, where we decompose the whole optimization problem into a sub-problem corresponding to the regularizer and another sub-problem corresponding to the structured hinge losses. For a large family of MTL problems, the first sub-problem has closed-form solutions. To solve the second sub-problem, we propose an efficient primal-dual algorithm via coordinate ascent. Extensive evaluation results demonstrate that, in a large family of MTL problems, the proposed MTL method of directly optimization evaluation metrics has superior performance gains against the corresponding baseline methods.

The ground vector $B_{c}^{\ast}$ meson has not yet been experimentally discovered until now. Besides the dominant electromagnetic decays, nonleptonic weak decays provide another choice to search for the mysterious $B_{c}^{\ast}$ mesons. Inspired by the potential prospects of $B_{c}^{\ast}$ mesons in future high-luminosity colliders, nonleptonic $B_{c}^{\ast}$ weak decays induced by bottom and charm quark decays are studied within the SM by using a naive factorization approach. It is found that for $B_{c}^{\ast}$ ${\to}$ $B_{s,d}{\pi}$, $B_{s,d}^{\ast}{\pi}$, $B_{s,d}{\rho}$, $B_{s}K$, $B_{s}^{\ast}K$, $B_{s}K^{\ast}$, ${\eta}_{c}(1S,2S){\pi}$, ${\eta}_{c}(1S,2S){\rho}$ and ${\psi}(1S,2S){\pi}$ decays, a few hundred and even thousand of events might be observable in CEPC, FCC-ee and LHCb@HL-LHC experiments., Comment: 18 pages

The current knowledge on the $D^{\ast}$ mesons are still inadequate. Encouraged by the positive development prospects of high-luminosity and high-precision experiments, the Cabibbo-favored nonleptonic $D^{\ast}$ ${\to}$ $\bar{K}{\pi}^{+}$, $\bar{K}^{\ast}{\pi}^{+}$, $\bar{K}{\rho}^{+}$ weak decays are studied with the naive factorization approach. It is found that branching ratios of these processes can reach up to ${\cal O}(10^{-10})$ or more, and can be accessible at STCF, CEPC, FCC-ee and LHCb@HL-LHC experiments in the future. It might even be possible to search for the $D^{{\ast}0}$ ${\to}$ $K^{{\ast}-}{\pi}^{+}$ and $K^{-}{\rho}^{+}$ decays at the running SuperKEKB experiments., Comment: 17 pages, 2 figures

A major limitation of fuzzy or neuro-fuzzy systems is their failure to deal with high-dimensional datasets. This happens primarily due to the use of T-norm, particularly, product or minimum (or a softer version of it). Thus, there are hardly any work dealing with datasets with dimensions more than hundred or so. Here, we propose a neuro-fuzzy framework that can handle datasets with dimensions even more than 7000! In this context, we propose an adaptive softmin (Ada-softmin) which effectively overcomes the drawbacks of ``numeric underflow" and ``fake minimum" that arise for existing fuzzy systems while dealing with high-dimensional problems. We call it an Adaptive Takagi-Sugeno-Kang (AdaTSK) fuzzy system. We then equip the AdaTSK system to perform feature selection and rule extraction in an integrated manner. In this context, a novel gate function is introduced and embedded only in the consequent parts, which can determine the useful features and rules, in two successive phases of learning. Unlike conventional fuzzy rule bases, we design an enhanced fuzzy rule base (En-FRB), which maintains adequate rules but does not grow the number of rules exponentially with dimension that typically happens for fuzzy neural networks. The integrated Feature Selection and Rule Extraction AdaTSK (FSRE-AdaTSK) system consists of three sequential phases: (i) feature selection, (ii) rule extraction, and (iii) fine tuning. The effectiveness of the FSRE-AdaTSK is demonstrated on 19 datasets of which five are in more than 2000 dimension including two with dimension greater than 7000. This may be the first time fuzzy systems are realized for classification involving more than 7000 input features.

In this paper, we calculate the vector, axial-vector and tensor form factors of $P\to T$ transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs). The self-consistency and Lorentz covariance of CLF QM with two types of correspondence schemes are investigated. The zero-mode effects and the spurious $\omega$-dependent contributions to the form factors of $P\to T$ transition are analyzed. Employing a self-consistent CLF QM, we present our numerical predictions for the vector, axial-vector and tensor form factors of $c\to (q,s)$~($q=u,d$) induced $D \to (a_2,K^*_2)$, $D_s \to (K^*_2,f'_{2})$, $\eta_c(1S) \to (D^*_2,D^*_{s2})$, $ B_c \to (B^*_2,B^*_{s2})$ transitions and $b\to (q,s,c)$ induced $B \to (a_2,K^*_2,D^*_2)$, $B_s \to (K^*_2,f'_2,D^*_{s2})$, $B_c \to (D^*_2,D^*_{s2},\chi_{c2}(1P))$, $\eta_b(1S) \to (B^*_2,B^*_{s2})$ transitions. Finally, in order to test the obtained form factors, the semileptonic $B\to \bar{D}_2^*(2460)\ell^+\nu_\ell$~($\ell=e,\mu$) and $\bar{D}_2^*(2460)\tau^+\nu_{\tau}$ decays are studied. It is expected that our results for the form factors of $P\to T$ transition can be applied further to the relevant phenomenological studies of meson decays., Comment: 41 pages, 7figures. arXiv admin note: text overlap with arXiv:1908.04677

We study the nonleptonic charmless $B_{u,d,s} \to K_0^*(1430)P$ $(P=K\,, \pi)$ and $ K_0^*(1430)V$ $ (V=K^*\,, \rho\,, \omega\,, \phi)$ decays. The amplitudes are calculated within the QCD factorization, and the non-perturbative quantities are evaluated by using a covariant light-front approach. The branching fractions and CP asymmetries of theses decay modes are calculated, some decay modes are first predicted, and some useful relations based on $SU(3)$ flavor symmetry are discussed. Comparing the theoretical results with the current available experimental data, it is found that $K_0^*(1430)$ can be described as the lowest-lying p-wave $(s,u/d)$ state rather than the first excited one., Comment: 38 pages, 3 figures

In this paper, we investigate the tensor form factors of $P\to P,\,S,\,V$ and $A$ transitions within the standard light-front (SLF) and the covariant light-front (CLF) quark models (QMs). The self-consistency and Lorentz covariance of CLF QM are analyzed via these quantities, and the effects of zero-mode are discussed. For the $P\to V$ and $A$ transitions, besides the inconsistence between the results extracted via longitudinal and transverse polarization states, which is caused by the residual $\omega$-dependent spurious contributions, we find and analyze a "new" self-consistence problem of the traditional CLF QM, which is caused by the different strategies for dealing deal with the trace term in CLF matrix element. A possible solution to the problems of traditional CLF QM is discussed and confirmed numerically. Finally, the theoretical predictions for the tensor form factors of some $c\to q,\,s$ and $b\to q,\,s\,,c$ ($q=u,d$) induced $P\to P,\,S,\,V$ and $A$ transitions are updated within the CLF QM with a self-consistent scheme., Comment: 34 pages, 9 figures and 7 tables. arXiv admin note: text overlap with arXiv:1908.04677

In this paper, we investigate the tree-dominated $\bar{B}^*_{u,d,s,c} \to V \ell^- \bar{\nu}_\ell$ ($V=D^*_{u,d}\,,D^*_s\,,J/\psi$ and $\ell=e\,,\mu\,,\tau$) decays in the Standard Model with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to the corresponding $\bar{B}^* \to P \ell^- \bar{\nu}_\ell$ and $\bar{B} \to V \ell^- \bar{\nu}_\ell$ decays, and moreover, the contribution of longitudinal polarization mode ($V$ meson) is relatively small, $\sim 30\%$, compared with the corresponding $B$ meson decays. We have also computed the branching fraction, lepton spin asymmetry, forward-backward asymmetry and ratio $R_V^{\ast(L)}\equiv \frac{\mathcal{B}(\bar{B}^*\to V\tau^- \bar{\nu}_\tau)}{\mathcal{B}(\bar{B}^*\to V \ell^{\prime-} \bar{\nu}_{\ell^{\prime}})}$ ($\ell'=e\,,\mu$). Numerically, the branching fractions of $\bar{B}^* \to V \ell^{\prime-} \bar{\nu}_{\ell^{\prime}}$ decays are at the level of ${\cal O}(10^{-7})$, and are hopeful to be observed by LHC and Belle-II experiments. The ratios $R_{D^*\,,D^*_s\,,J/\psi}^{\ast(L)}$ have relatively small theoretical uncertainties and are close to each other, $R^{*(L)}_{D^*}\simeq R^{*(L)}_{D^*_s}\simeq R^{*(L)}_{J/\psi} \simeq [0.26,0.27]~([0.27,0.29])$, which are a bit different from the predictions in some previous works. The future measurements are expected to make tests on these predictions., Comment: 22 pages, 3 figures

In this paper, we calculate the matrix element and form factors of vector-to-vector ($V'\to V'$) transition within the standard light-front~(SLF) and covariant light-front~(CLF) quark models~(QMs), and investigate the self-consistency and Lorentz covariance of the CLF QM within two types of correspondences between the manifest covariant Bethe-Salpeter approach and the LF approach. The zero-mode and valence contributions to the form factors of $V'\to V'$ transition in the CLF QM and their relation to the SLF results are analyzed, and the main conclusions obtained via the decay constants of vector and axial-vector mesons and form factors of $P\to V$ transition in the previous works are confirmed again. Furthermore, we present our numerical predictions for the form factors of $c\to (q,s)$ ($q=u,d$) induced $D^*\to (K^*\,,\rho)$, $D^*_s\to (\phi\,,K^*)$, $J/\Psi\to (D^*_s\,,D^*)$, $B^*_c\to (B^*_s\,,B^*)$ transitions and $b\to (q,s,c)$ induced $B^*\to (D^*\,,K^*\,,\rho)$, $B^*_s\to (D^*_s\,,\phi\,,K^*)$, $B^*_c\to (J/\Psi\,,D^*_s\,,D^*)$, $\Upsilon(1S)\to (B_c^*\,,B_s^*\,,B^*)$ transitions, which can be applied further to the relevant phenomenological studies of meson decays., Comment: 47pages, 6 figures, 10 tables. Revised version; Accepted for publication in JHEP

Motivated by the rapid development of heavy flavor physics experiment, we study the tree-dominated nonleptonic $\bar{B}_{u,d,s}^* \to D_{u,d,s}^*V$~($V=D^{*-},D_s^{*-},K^{*-},{\rho}^-$) decays within the factorization approach. The relevant transition form factors are calculated by employing the covariant light-front quark model. The helicity amplitudes are calculated and analyzed in detail, and a very clear hierarchy structure $ |H_{-0}| \approx 2|H_{00}| > |H_{0-}|\approx|H_{--}|>|H_{0+}|\approx|H_{++}|$ is presented. The branching fractions are computed and discussed. Numerically, the CKM-favored $\bar{B}^*_q\to D^*_q \rho^{-}$ and $D^*_q D_s^{*-}$ decays have relatively large branching fractions, $\gtrsim {\cal O}(10^{-8})$, and are hopeful to be observed by LHC and Belle-II experiments in the future., Comment: 19pages

With the potential for the improvements of measurement precision,the refinement of theoretical calculation on hadronic $B$ weak decays is necessary. In this paper, we study the contributions of $B$ mesonic distribution amplitude ${\Phi}_{B2}$ within the QCD factorization approach, and find that ${\Phi}_{B2}$ contributes to only the nonfactorizable annihilation amplitudes for the $B$ ${\to}$ $PP$ decays ($P$ denotes the ground $SU(3)$ pseudoscalar mesons). Although small, the ${\Phi}_{B2}$ contributions might be helpful for improving the performance of the QCD factorization approach, especially for the pure annihilation $B_{d}$ ${\to}$ $K^{+}K^{-}$ and $B_{s}$ ${\to}$ ${\pi}^{+}{\pi}^{-}$ decays., Comment: 13pages,8figures

We investigate the self-consistency and Lorentz covariance of the covariant light-front quark model~(CLF QM) via the matrix elements and form factors~(${\cal F}=g$, $a_{\pm}$ and $f$) of $P\to V$ transition. Two types of correspondence schemes between the manifest covariant Bethe-Salpeter approach and the light-front quark model are studied. We find that, for $a_{-}(q^2)$ and $f(q^2)$, the CLF results obtained via $\lbd=0$ and $\pm$ polarization states of vector meson within the traditional type-I correspondence scheme are inconsistent with each other; and moreover, the strict covariance of the matrix element is violated due to the nonvanishing spurious contributions associated with noncovariance. We further show that such two problems have the same origin and can be resolved simultaneously by employing the type-II correspondence scheme, which advocates an additional replacement $M\to M_0$ relative to the traditional type-I scheme; meanwhile, the results of ${\cal F}(q^2)$ in the standard light-front quark model~(SLF QM) are exactly the same as the valence contributions and equal to numerally the full results in the CLF QM, {\it i.e.}, $[{\cal{F}}]_{\rm SLF}=[{\cal{F}}]_{\rm val.}\doteq[{\cal{F}}]_{\rm full}$. The numerical results for some $P\to V$ transitions are updated within the type-II scheme. Above findings confirm the conclusion obtained via the decay constants of vector and axial-vector mesons in the previous works., Comment: 28 pages, 3 figures and 5 tables

In this paper, we test the self-consistencies of the standard and the covariant light-front quark model and study the zero-mode issue via the decay constants of pseudoscalar ($P$), vector ($V$) and axial-vector ($A$) mesons, as well as the $P\to P$ weak transition form factors. With the traditional type-I correspondence between the manifestly covariant and the light-front approach, the resulting $f_{V}$ as well as $f_{^1\!A}$ and $f_{^3\!A}$ obtained with the $\lbd=0$ and $\lbd=\pm$ polarization states are different from each other, which presents a challenge to the self-consistency of the covariant light-front quark model. However, such a self-consistency problem can be "resolved" within the type-II scheme, which requires an additional replacement $M\to M_0$ relative to the type-I case. Moreover, the replacement $M\to M_0$ is also essential for the self-consistency of the standard light-front quark model. In the type-II scheme, the valence contributions to the physical quantities~(${\cal Q}$) considered in this paper are alway the same as that obtained in the standard light-front quark model, $[{\cal Q}]_{\rm val.}=[{\cal Q}]_{\rm SLF}$, and the zero-mode contributions to $f_{V,^1\!A,^3\!A}$ and $f_-(q^2)$ exist only formally but vanish numerically, which implies further that $[{\cal Q}]_{\rm val.}\dot{=} [{\cal Q}]_{\rm full}$. In addition, the manifest covariance of the covariant light-front quark model is violated in the traditional type-I scheme, but can be recovered by taking the type-II scheme., Comment: 37 pages, 5 figures, to be published in Phys. Rev. D

The $B_{u}$ ${\to}$ ${\psi}M$ decays are studied with the perturbative QCD approach, where the psion ${\psi}$ $=$ ${\psi}(2S)$, ${\psi}(3770)$, ${\psi}(4040)$ and ${\psi}(4160)$, and the light meson $M$ $=$ ${\pi}$, $K$, ${\rho}$ and $K^{\ast}$. The factorizable and nonfactorizable contributions, and the $S$-$D$ wave mixing effects on the psions are considered in the calculation. With appropriate inputs, the branching ratios for the $B_{u}$ ${\to}$ ${\psi}K$ decays are generally coincident with the experimental data within errors. However, due to the large theoretical and experimental errors, it is impossible for the moment to give a severe constraint on the $S$-$D$ wave mixing angles., Comment: revtex, 29 pages, 4 figures

The significant divergence between the SM predictions and experimental measurements for the ratios, $R_{D^{(*)}}\equiv \mathcal{B}(\bar{B}\to D^{(*)}\tau^- \bar{\nu}_\tau)/ \mathcal{B}(\bar{B}\to D^{(*)} \ell^{\prime-} \bar{\nu}_{\ell^{\prime}})$ with $(\ell^{\prime}=e\,,\mu)$, implies possible hint of new physics in the flavour sector. In this paper, motivated by the "$R_{D^{(*)}}$ puzzle" and abundant $B^*$ data samples at high-luminosity heavy-flavor experiments in the future, we try to probe possible effects of new physics in the semileptonic $\bar{B}^*_{u,d,s} \to P \ell^- \bar{\nu}_\ell$ $(P=D\,,D_s\,,\pi\,,K)$ decays induced by $b \to (u,\,c)\ell^- \bar{\nu}_{\ell}$ transitions in the model-independent vector and scalar scenarios. Using the spaces of NP parameters obtained by fitting to the data of $R_{D}$ and $R_{D^{*}}$, the NP effects on the observables including branching fraction, ratio $R_P^{\ast}$, lepton spin asymmetry and lepton forward-backward asymmetry are studied in detail. We find that the vector type couplings have large effects on the branching fraction and ratio $R_P^{\ast}$. Meanwhile, the scalar type couplings provide significant contributions to all of the observables. The future measurements of these observables in the $\bar{B}^* \to P \ell^- \bar{\nu}_\ell$ decays at the LHCb and Belle-II could provide a way to crosscheck the various NP solutions to the "$R_{D^{(*)}}$ puzzle"., Comment: 24 pages, 4 figures

In this paper, we study the non-leptonic $B_{c}\to J/\psi V$ and $B_{c}^{*}\to\eta_{c}V$~$(V=\rho\,,K^{*})$ weak decays in the framework of QCD factorization. In the evaluation, the form factors are calculated by using the Bauer-Stech-Wirbel model and the light-front quark model, respectively. Besides the longitudinal amplitude, the power-suppressed transverse contributions are also evaluated at next-to-leading order. The predictions for the observables of $B_{c}\to J/\psi V$ and $B_{c}^{*}\to\eta_{c}V$ decays are presented. We find that the NLO QCD contribution presents about $ 8\%$ correction to the branching ratios, and the longitudinal polarization fractions of these decays are at the level of $(80\sim90)\%$. In addition, we suggest direct measurements on some useful ratios, $R_{K^{*}/\rho}^{(\lambda=0)}$ and $\widetilde{R}^{(\lambda=0)}_{K^{*}/\rho}$, which are very suitable for test the consistence between theoretical prediction and data because their theoretical uncertainties can be well-controlled., Comment: 21 pages, 5 figures; To be published in Journal of Physics G

In this paper we extend our analyses of the decay constant and distribution amplitude with an improved holographic wavefunction to the heavy-light pseudoscalar mesons. In the evaluations, the helicity-dependence of the holographic wavefunction is considered; and an independent mass scale parameter is employed to moderate the strong suppression induced by the heavy quark. Under the constraints from decay constants and masses of pseudoscalar mesons, the $\chi^2$-analyses for the holographic parameters exhibit a rough consistence with the results obtained by fitting the Regge trajectory. With the fitted parameters, the results for the decay constants and distribution amplitudes are presented. We then show their application in evaluating the $B_{d,s}\to D_{d,s}P$ decays, in which the power-suppressed spectator scattering and weak annihilation corrections are first estimated. Numerically, the spectator scattering and weak annihilation corrections present a negative shift of about $ 0.7\%$ on the branching fractions; while, the predictions are still larger than the experimental data. Such small negative shift confirms the estimation based on the power counting rules., Comment: 10 pages, 5 figures

We calculate the decay constants of light and heavy-light pseudoscalar and vector mesons with improved soft-wall holographic wavefuntions, which take into account the effects of both quark masses and dynamical spins. We find that the predicted decay constants, especially for the ratio $f_V/f_P$, based on light-front holographic QCD, can be significantly improved, once the dynamical spin effects are taken into account by introducing the helicity-dependent wavefunctions. We also perform detailed $\chi^2$ analyses for the holographic parameters ({\it i.e.} the mass-scale parameter $\kappa$ and the quark masses), by confronting our predictions with the data for the charged-meson decay constants and the meson spectra. The fitted values for these parameters are generally in agreement with those obtained by fitting to the Regge trajectories. At the same time, most of our results for the decay constants and their ratios agree with the data as well as the predictions based on lattice QCD and QCD sum rule approaches, with only a few exceptions observed., Comment: 27 pages, 4 figures and 3 tables; typos corrected, references added, final version published in Chinese Physics C

The rare cascade $B_{s}$ ${\to}$ ${\phi}f_{0}(980)$ ${\to}$ ${\phi}\,{\pi}^{+}{\pi}^{-}$ decay is studied with the perturbative QCD approach based on the formula for the quasi two-body decay, where the two-pion pair originates from the $S$-wave resonant $f_{0}(980)$ state. It is found that with the introduction of the nonperturbative two-pion distribution amplitudes and the Flatt\'{e} parameterization of the scalar form factor for the $f_{0}(980)$ resonance, the branching ratio in the mass range 400 MeV $<$ $m({\pi}^{+}{\pi}^{-})$ $<$ 1600 MeV is ${\cal B}_{\rm theo}(B_{s}^{0}\, {\to}\,{\phi}\,f_{0}(980)\,{\to}\,{\phi}\,{\pi}^{+}\,{\pi}^{-})$ $=$ $[1.31_{-0.31}^{+0.40}(a_{{\pi}{\pi}}){}_{-0.16}^{+0.19}(m_{b}) {}_{-0.09}^{+0.10}(\text{CKM})]{\times}10^{-6}$, where the uncertainties come from the parameter $a_{{\pi}{\pi}}$ of the two-pion distribution amplitudes, the $b$ quark mass $m_{b}$, the Cabibbo-Kobayashi-Maskawa (CKM) factors, respectively. This result agrees with the recent LHCb measurement within uncertainties, ${\cal B}_{\rm exp}(B_{s}^{0}\,{\to}\,{\phi}\, f_{0}(980)\,{\to}\,{\phi}\,{\pi}^{+}\,{\pi}^{-})$ $=$ $(1.12{\pm}0.16^{+0.09}_{-0.08}{\pm}0.11){\times}10^{-6}$, where the errors are statistical, systematic and from the normalization, respectively., Comment: 27 pages, 2 figures