Based on the predictions of the relevant form factors from the covariant light-front quark model, we show the branching fractions for the \(D (D_s) \rightarrow (P,\,S,\,V,\,A)\,\ell \nu _\ell \) (\(\ell =e\) or \(\mu \)) decays, where P denotes the pseudoscalar meson, S the scalar meson with a mass above 1 GeV, V the vector meson and A the axial-vector one. Comparison with the available experimental results are made, and we find an excellent agreement. The predictions for other decay modes can be tested in a charm factory, e.g., the BESIII detector. The future measurements will definitely further enrich our knowledge of the hadronic transition form factors as well as the inner structure of the even-parity mesons (S and A).

The null signal from collider and dark matter (DM) direct detector experiments makes the interaction between DM and visible matter too small to reproduce the correct relic density for many thermal DM models. The remaining parameter space indicates that two almost degenerated states in the dark sector, the inelastic DM scenario, can co-annihilate in the early universe to produce the correct relic density. Regarding the direct detection of the inelastic DM scenario, the virialized DM component from the nearby halo is nonrelativistic and not able to excite the DM ground state, even if the relevant couplings can be considerable. Thus, a DM with a large mass splitting can evade traditional virialized DM direct detection. In this study, we connect the concept of cosmic-ray accelerated DM in our Milky Way and the direct detection of inelastic scattering in underground detectors to explore spectra that result from several interaction types of the inelastic DM. We find that the mass splitting $$ \delta <\mathcal{O}\left(1\ \mathrm{GeV}\right) $$δ < O 1 GeV can still be reachable for cosmic ray accelerated DM with mass range 1 MeV < $$ {m}_{\chi_1} $$m χ 1 < 100 GeV and sub-GeV light mediator using the latest PandaX-4T data, even though we conservatively use the astrophysical parameter (effective length) D_eff = 1 kpc.

There are some corrections on the last line of Table. 1 and 2 for the decays involving the $$K_1(1270)$$K1(1270) and $$K_1(1400)$$K1(1400) in the original publication.

The semileptonic decay of heavy flavor mesons offers a clean environment for extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements, which describes the CP-violating and flavor changing process in the Standard Model. The involved form factors where the dynamical information is encoded play an essential role in achieving any conclusive statement. That is, the knowledge of the form factors should be under good control, requiring one to examine more observables in addition to the branching fraction. In this paper, we provide the mean value and the q²-dependent shape for further observables [differential decay distribution (dΓ/dq²), forward-backward asymmetry $$ \left({\mathcal{A}}_{FB}^{ls}\right) $$A FB ls , longitudinal $$ \left({P}_L^l\right) $$P L l and transverse $$ \left({P}_T^l\right) $$P T l polarization of a charged lepton, longitudinal polarization of a vector meson in the final state $$ \left({F}_L^l(V)\right) $$F L l V , leptonic convexity parameter $$ \left({C}_F^l\right) $$C F l , and trigonometric moments $$ \left({W}_i^l\right) $$W i l in the decay of D_(s) and B_(s) to P/Vl⁺ν_l (l = e, μ or τ)], based on the predictions of the relevant form factors from the covariant light-front quark model. P and V denote the pseudoscalar and vector meson, respectively. As a comparison, we find a good agreement with the results from the covariant confining quark model and the relativistic quark model in the literature. As it has been observed that the $$ {P}_L^l $$P L l and $$ {F}_L^l(V) $$F L l V are crucial quantities to discriminate various New Physics models, the reexamination of these observables from a different method is also essential and necessary.

We reanalyze the problems in the assignment of $3{}^3{S}_1$ and $4{}^3{S}_1$ light mesons, which have not yet been well established with the $q\overline{q}$ quark model. Regge trajectories and the ${}^3{P}_0$ decay model are used, respectively, to study the mass and width of the observed states and predict the missing ones. By comparing our calculations with the latest experiments, we suggest that the inconsistent data of $\rho (2150)$ may include two similar structures, $\rho (4{{}^{3}S}_1)$ and $\omega (4{{}^{3}S}_1)$. In addition, the problem of the $K^{*}(2{{}^{3}S}_1)$ assignment, with two observed states $K^{*}(1410)$ and $K^{*}(1680)$, is investigated, with several possible explanations.

The form factors of the semileptonic $B$, $B_s$, and $B_c$ meson decays are calculated in the framework of the relativistic quark model based on the quasipotential approach in QCD. They are expressed through the overlap integrals of the meson wave function. All relativistic effects are consistently taken into account. The momentum transfer $q^2$ behavior of form factors is determined in the whole accessible kinematical range. We do not use any extrapolations, heavy quark $1/m_Q$ expansion, or model assumptions about the shape of form factors. Convenient analytic expressions of the form factors are given, which very accurately reproduce the numerical results of our calculation. On the basis of these form factors and helicity formalism, the differential and total branching fractions of various semileptonic decays of bottom meson are calculated. The mean values of the forward-backward asymmetry $⟨A_{\mathrm{FB}}⟩$, lepton-side convexity parameter $⟨C_F^{\ell }⟩$, longitudinal $⟨P_L^{\ell }⟩$ and transverse $⟨P_T^{\ell }⟩$ polarization of the charged lepton, and the longitudinal polarization fraction $⟨F_L⟩$ for final-state vector meson are also evaluated. We present a detailed comparison of the obtained predictions with the calculations based on the covariant light-front quark model and confront them to available lattice QCD and experimental data. It is found that although both models predict close values of the total branching fractions, the differential distributions and forward-backward asymmetry and polarization parameters differ significantly, especially for the heavy-to-light semileptonic decays. We identify observables which measurement can help to discriminate between models.