Narrow Results

The decay constants of pseudoscalar and vector heavy–light mesons are calculated in the framework of the relativistic quark model with the completely relativistic treatment of the light quark. It is argued that relativistic effects play a significant role. Good agreement of the model predictions with recent lattice and QCD sum rule calculations as well as available experimental data are found.

Two-photon decay rates of pseudoscalar, scalar and tensor states of charmonium and bottomonium are calculated in the framework of the relativistic quark model. Both relativistic effects and one-loop radiative corrections are taken into account. The obtained results are compared with other theoretical predictions and available experimental data.

The hyperfine splitting in heavy quarkonia is considered in its relation to the leptonic decay rates with the account of relativistic and radiative corrections. The calculated decay rates agree well with the available experimental data, while the predicted η_c(2S) mass is significantly smaller than the value measured recently by the Belle collaboration.

The charmonium mass spectrum is considered in the framework of the constituent quark model with the relativistic treatment of the c quark. The obtained masses are in good agreement with the existing experimental data including the mass of η_c(2S).

The masses of the S-wave mesons consisting of the light (u, d, s) quarks are calculated within the constituent quark model. The relativistic Schrödinger-like equation with a confining potential is numerically solved for the complete relativistic potential including both spin-independent and spin-dependent terms. The obtained masses of the ground state π, ρ, K, K* and ϕ mesons and their first radial excitations are in a reasonably good overall agreement with experimental data.

The relativistic model of the ground state and excited heavy tetraquarks with hidden bottom is formulated within the diquark–antidiquark picture. The diquark structure is taken into account by calculating the diquark–gluon vertex in terms of the diquark wave functions. Predictions for the masses of bottom counterparts to the charm tetraquark candidates are given.

Semileptonic and leptonic B decays are analyzed in the framework of the relativistic quark model. Special attention is paid to the decays involving τ lepton. It is found that the calculated particular decay branching fractions are consistent with available experimental data within error bars. However, the predicted and recently measured ratios R(D^(*)) of the B→D^(*)τν_τ and B→D^(*)lν_l branching fractions differ by 1.75σ for R(D) and by 2.4σ for R(D*).

Confinement and spontaneous breaking of chiral symmetry are assumed to generate the governing degrees of freedom of low-energy quantum chromodynamics. On this basis a relativistic constituent-quark model is constructed and formulated along an invariant mass operator within Poincaré-invariant quantum mechanics. The model is effectively applied to the spectroscopy of all known baryons of flavors u, d, s, c and b. The mass-operator eigenstates are furthermore tested with regard to the baryon electromagnetic and axial form factors. Through using the point form of relativistic quantum mechanics, these observables are obtained in a manifestly covariant manner. For all light and strange baryon ground states the electroweak structures are reproduced either in good agreement with phenomenology or, if no experimental data exist, in consistency with results available from lattice quantum chromodynamics. It is concluded that the relativistic constituent-quark model, relying on {QQQ} Fock states only, provides a universal framework for the description of low-energy baryons. The most important ingredients are spontaneous chiral-symmetry breaking and strict relativistic invariance.

The form factors of the rare ${\mathrm{\Lambda }}_b\to n{l}^{+}{l}^{-}$ decays are calculated in the framework of the relativistic quark–diquark picture of baryons with the consistent account of the relativistic effects. Their momentum transfer squared dependence is determined explicitly in the whole accessible kinematical range. The decay branching fractions, forward–backward asymmetries and the fractions of longitudinally polarized dileptons are determined. The branching fraction of the rare ${\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-}$ decay are found to be $\mathrm{\text{Br}}({\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-})=(3.75\pm 0.38)\times 10^{-8}$ and thus could be measured at the LHC. Prediction for the branching fraction of the rare radiative ${\mathrm{\Lambda }}_b\to n\gamma$ decay is also given.

Recently, the LHCb collaboration put the upper limit on the ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma$ decay branching ratio $\mathrm{\text{Br}}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\gamma )<1.3\times 10^{-4}$. The measured value is below the light-cone sum rule prediction. In this paper, the rare radiative decay of the ${\mathrm{\Xi }}_b^{-}$ baryon is studied in the framework of the relativistic quark model based on the quasipotential approach and QCD. The decay form factors are calculated with the comprehensive account of the relativistic effects. The obtained result for the branching ratio is found to be below the upper limit set by LHCb and is consistent with theoretical predictions based on the SU(3) flavor-symmetry, light-front quark model and light-cone QCD sum rules in full theory within theoretical uncertainties.

Based on the relativistic quark model and the infinitesimally shifted Gaussian basis function method, we investigate the mass spectra of double-bottom baryons systematically. In the $\rho$-mode which appears lower in energy than the other excited modes, we obtain the allowed quantum states and perform a systematic study of the mass spectra of the ${\mathrm{\Xi }}_{bb}$ and ${\mathrm{\Omega }}_{bb}$ families. We analyze the root mean square radii and quark radial probability density distributions to deeply understand the structure of the heavy baryons. Meanwhile, the mass spectra allow us to successfully construct the Regge trajectories in the $(J,M^2)$ plane. We also predict the masses of the ground states of double-bottom baryons and discuss the differences between the structures of our spectra and those from other theoretical methods. At last, the shell structure of the double-bottom baryon spectra is shown from which one could get a bird’s-eye view of the mass spectra. In this paper, we also make a hypothesis that the heavy baryon excitation may be dominated by the excitation of heavy quarks in the heavy quark limit. It could help to deepen the understanding of heavy baryons structure.

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.

Within the dispersion relation approach we give the double spectral representation for space-like and time-like B → f₀(980) and D → f₀(980) transition form factors in the whole q² range. The spectral densities, being the input of the dispersion relations, are obtained from a triangle diagram of relativistic constituent quarks.

A relativistic power-law potential model of independent quarks is used to study the leptonic decays of neutral vector mesons. Here, the transition probability amplitude for leptonic decay of meson is determined from the momentum distribution function which is found from the assumption of a strong correlation existing between the momenta of quark and antiquark inside the meson. The model parameters are first determined from the application of the model to study the ground state spectra of ρ, ω, ϕ, ψ and ϒ mesons together with the radiative decay widths of mesons. The same model with no adjustable parameters is then used to evaluate the leptonic decay widths and the electromagnetic decay constants for the vector mesons ρ, ω, ϕ, ψ and ϒ. The calculated results are in remarkable agreement with the corresponding experimental values.

An independent quark model with a relativistic power-law potential is used to study the weak leptonic decays of light and heavy pseudoscalar mesons. The partial decay width and the decay constant for the weak leptonic decay are derived from the quark–antiquark momentum distribution amplitude which is obtained from the bound quark eigenfunction with the assumption of a strong correlation existing between quark–antiquark momenta inside the decaying meson in its rest frame. The model parameters are first determined from the application of the model to study the ground state hyperfine splitting of ρ, K, D, D_s, B, B_s and B_c mesons. The same model with no adjustable parameters is then used to evaluate the decay constants f_M and the decay widths of pseudoscalar mesons. The model predictions agree quite well with the available experimental data as well as with those of several other models. The decay constant for pion and kaon are obtained as f_π = 132 MeV and f_k = 161 MeV which closely agree with experimental values. But in case of heavier mesons for which experimental data are not yet available, the present model gives its predictions as f_BC > f_BS > f_B, f_DS > f_D, f_D > f_B and f_π > f_B which are in conformity with most of other model predictions. The model predictions of the corresponding decay widths and the branching ratios for the and decay modes are in close agreement with the available experimental data.

In this paper, we investigate the mass spectra of bottom-charm baryons systematically, where the relativistic quark model and the infinitesimally shifted Gaussian basis function method are employed. Our calculation shows that the $\rho$-mode appears lower in energy than the other excited modes. According to this feature, the allowed quantum states are selected and a systematic study of the mass spectra for ${\mathrm{\Xi }}_{bc}^{\prime }$ (${\mathrm{\Xi }}_{bc}$) and ${\mathrm{\Omega }}_{bc}^{\prime }$ (${\mathrm{\Omega }}_{bc}$) families is performed. The root mean square radii and quark radial probability density distributions of these baryons are analyzed as well. Next, the Regge trajectories in the $(J,M^2)$ plane are successfully constructed based on the mass spectra. At last, we present the structures of the mass spectra, and analyze the difficulty and opportunity in searching for the ground states of bottom-charm baryons in experiment.

We have studied the chiral soliton model in a thermal vacuum. The soliton equations are solved at finite temperature and density. The temperature or density dependent soliton solutions are presented. The physical properties of baryons are derived from the soliton solutions at finite temperature and density. The temperature or density dependent variation of the baryon properties are discussed.

We analyze the tauonic semileptonic baryon decays ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}+{\tau }^{-}+{\bar{\nu }}_{\tau }$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the ${\mathrm{\Lambda }}_c^{+}$ and the ${\tau }^{-}$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.

We investigate the radiative transitions of charmonium system in the framework of the relativistic covariant quark model, where the center of mass motion of the hadron is treated in a manifestly covariant way. We discuss the obtained results in comparison with that in the nonrelativistic model.