Sea quark contributions to nucleon electromagnetic form factors with the nonlocal chiral effective Lagrangian

The sea quark contributions to the nucleon electromagnetic form factors of the up,down and strange quarks are studied with the nonlocal chiral effective Lagrangian.Both octet and decuplet intermediate states are included in the one loop calculations.Compared with the strange quark form factors,although their signs are the same,the absolute value of the light quark form factors are much larger.For both the electric and magnetic form factors,the contribution of the d quark is larger than of the u quark.The current lattice simulations of the light sea quark form factors are in between our results for the u and d quarks.     

Light Flavor Vector and Pseudo Vector Mesons from a Light-Cone QCD Inspired Effective Hamiltonian Model with SU（3） Flavor Mixing Interactions

Based on the light-cone effective Hamiltonian with confining potential and SU （3） flavor mixing interactions, the flavor mixing mesons on the u, d, and s quark sectors are investigated. The mass eigen equations of the flavor mixing vector and pseudo vector mesons are solved. The calculated masses are in good agreement with the experimental data.     

I=1/2 low-lying mesons in lattice QCD

Using a conventional constituent-quark model,I=1/2 scalarκ,vector K*(892),and axial vector K1mesons are studied in the asqtad-improved staggered fermion with wall-source and point-sink interpolators.The mass ratio of mκ/mK*(892)is numerically confirmed to apparently vary with quark mass,and the experimental ordering mK*(892)mκholds elegantly when the light u/d quark masses are sufficiently small,while the valence strange quark mass is fixed to its physical value.We also get reasonable signals for the K1 meson suggested by the SCALAR Collaboration from lattice QCD.The computations are conducted with the MILC Nf=3 flavor gauge configurations at three lattice spacings:a≈0.15,0.12,and 0.09 fm.     

Heavy mesons in the Nambu-Jona-Lasinio model

We propose an extended Nambu-Jona-Lasinio model to include heavy mesons with heavy quark symmetry.The quark current-current interaction is generalized to include the heavy quark currents. In order to comply with the heavy quark spin symmetry at the heavy quark limit,the dependence of the quark mass on the interaction strength is introduced. The light and heavy pseudo-scalar and vector mesons,their masses and the weak decay constants are calculated in the unified frame.     

Quenched Charmed Meson Spectra Using Tadpole Improved Quark Action on Anisotropic Lattices

Charmed meson charmonium spectra are studied with improved quark actions on anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion relations for four lowest lattice momentum modes with quark mass values ranging from the strange quark to charm quark with three different values of gauge coupling β and four different values of bare speed of light v. With the bare speed of light parameter v tuned in a mass-dependent way, we study the mass spectra of D, Ds, ηc, D^＊, D^＊s and J/ψ mesons. The results extrapolated to the continuum limit are compared with the experiment, and a qualitative agreement is found.     

In-Medium Nucleon Electromagnetic Form Factors in Vector Meson Dominance Model

We study medium modifications of the nucleon electromagnetic form factors in the vector meson dominance model. The in-medium vector meson masses are taken from a chiral SU(3) model. We find that the electric and magnetic form factors of the bound nucleon deviate considerably from those of the free nucleon. Our results are comparable to the results from the quark meson coupling model approach and are consistent with present experimental limits.     

D and Ds in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed （D） and charmed strange （Ds） mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1（13D1） and the 3（13D3） Ds agree well with those of recently observed Ds1（2700）± and DsJ（2860）, respectively.     

Ratio of a strange quark mass ms to up or down quark mass mu,d predicted by a quark propagator in the framework of the chiral perturbation theory

Based on the fully dressed quark propagator and chiral perturbation theory, we study the ratio of the strange quark mass ms to up or down quark mass mu,d . The ratio is related to the determination of quark masses which are fundamental input parameters of QCD Lagrangian in the Standard Model of particle physics and can not be directly measured since the quark is confined within a hadron. An accurate determination of these QCD free parameters is extremely important for both phenomenological and theoretical applications. We begin with a brief introduction to the non-perturbation QCD theory, and then study the mass ratio in the framework of the chiral perturbation theory (χPT) with a parameterized fully dressed quark propagator which describes confining fully dressed quark propagation and is analytic everywhere in the finite complex p2-plane and has no Lehmann representation so there are no quark production thresholds in any theoretical calculations of observable data. Our prediction for the ratio ms/mu,d is consistent with other model predictions such as Lattice QCD, instanton model, QCD sum rules and the empirical values used widely in the literature. As a by-product of this study, our theoretical results, together with other predictions of physical quantities that used this quark propagator in our previous publications, clearly show that the parameterized form of the fully dressed quark propagator is an applicable and reliable approximation to the solution of the Dyson-Schwinger Equation of quark propagator in the QCD.     

D and D_s in mass loaded flux tube

Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1(13D1) and the 3(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.     

Screening of light mesons and charmonia at high temperature

We present lattice QCD results for the screening masses of light mesons and charmonia. The lattice computations were performed with 2 + 1 flavors of improved staggered quarks using quark masses which correspond to realistic pion and kaon masses at zero temperature. For the light quark sector we have found that the screening masses in the pseudo-scalar and the isovector scalar channels do not become degenerate at the chiral crossover temperature indicating an effective non-restoration of the axial symmetry. Also the splitting between the vector and the pseudo-scalar screening masses persists even in the limit of zero lattice spacing and at a moderately high temperature around 420 MeV. In the charmonium sector our investigation shows that the screening masses of the pseudo-scalar and the vector charmonia are almost (within a few percent) equal to their zero temperature masses for temperatures less than 300 MeV. We also present results for the charmonium screening masses using periodic boundary conditions along the temporal direction and discuss their implications.     

Masses and electroweak properties of light mesons in the relativistic quark model

The masses, pseudoscalar and vector weak decay constants and electromagnetic form factors of light S-wave mesons are studied in the framework of the relativistic quark model based on the quasipotential approach. We use the same model assumptions and parameters as in our previous investigations of heavy meson and baryon properties. The masses and wave functions of the ground state and radially excited π, ρ, K, K^* and φ mesons, obtained by solving numerically the relativistic Schrödinger-like equation with the complete relativistic qq? potential including both spin-independent and spin-dependent terms, are presented. Novel relativistic expressions for the weak decay constants of the pseudoscalar and vector mesons are derived. It is shown that the intermediate negative-energy quark states give significant contributions which essentially decrease the decay constants bringing them in agreement with experimental data. The electromagnetic form factors of the pion, charged and neutral kaon are calculated in a broad range of the space-like momentum transfer. The corresponding charge radii are determined. All results agree well with the available experimental data.     

Inclusive production cross sections of resonances in 32 GeV/c K+p interactions

The inclusive production of resonances is systematically studied in K⁺p interactions at 32 GeV/c. Total production cross sections are given for three baryon resonances, five vector and three 2⁺ tensor mesons. We also compare the central and fragmentation components of the total production cross sections with quark model predictions.     

Semileptonic B decays into even parity charmed mesons

By using a constituent quark model we compute the form factors relevant to semileptonic transitions of the B mesons into low-lying p-wave charmed mesons. We evaluate the q² dependence of these form factors and compare them with other model calculations. The Isgur–Wise functions τ_1/2 and τ_3/2 are also obtained in the heavy quark limit of our results. PACS 13.25.Hw; 12.39.Hg; 12.39.Jh     

A relativistic quark model for mesons with an instanton-induced interaction

We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the U _A(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like π⁺/K ⁺↦e ⁺υ_eγ and 0^-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the K _?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data. Received: 28 August 2000 / Accepted: 12 September 2000     

A static calculation of radiative decay widths of mesons in a potential model of independent quarks

Taking a relativistic potential model of independent quarks with its parameters determined from a fit to the mass splittings of ground state mesons in the strange, charm and bottom flavor sector, we perform a ‘static’ calculation of decay widths for the radiative transitions of mesons within the conventional picture of photon emission by a confined quark and/or antiquark. The results obtained in most of the cases of light mesons are in an overall agreement with the experimental values. The predictions in heavy meson decays are comparable to those of other model calculations.     

Radiative decays and transition form factors of strange mesons in the relativistic constituent quark model

Motivated by the recent lattice QCD results indicating that the topological charge contribution to the flavor singlet axial vector current can be traded off by the constituent quark masses, we investigate the radiative decays of pseudoscalar (π,K, η, η′), vector (ρ,K*, ω, ?) and axial vector (A ₁) mesons using a simple relativistic constituent quark model. For both simplicity and relativity, we take advantage of the distinguished features in the light-cone quantization method: (1) the Fock-state expansion of meson wavefunctions are not contaminated by the vacuum fluctuation, (2) the assignment of meson quantum numbers are given by the Melosh transformation. Except the well-known constituent quark masses of (u,d,s) quarks and the spin-averaged meson masses, the only parameter in the model is the gaussian parameter β which determines the broadness (or sharpness) of radial wavefunction. The computed decay widths and the transition form factors of ρ, ω → π(η)γ*,K* →Kγ* andA ₁ → πγ* at 0≤Q ²≤5 GeV² and π⁰(η) → γ*γ at 0≤Q ²≤3 GeV² are in a remarkably good agreement with the experimental data and the result forA ₁ ⁺ → π₊ γ* transition is quite consistent with the experiments of pion scattering on a nucleus using Primakoff effect. This model is potentially useful in the cocktail analyses of the dilepton productions in proton-proton, proton-nucleus and nucleus-nucleus collisions at SPS energies and a little above.     

Axial resonances in the open and hidden charm sectors

A SU(4) flavor symmetrical Lagrangian is constructed for the interaction of the pseudo-scalar mesons with the vector mesons. SU(4) symmetry is broken to SU(3) by suppression of terms in the Lagrangian where the interaction should be driven by charmed mesons. Chiral symmetry can be restored by setting this new SU(4) symmetry-breaking parameters to zero. Unitarization in coupled channels leads to the dynamical generation of resonances. Many known axial resonances can be identified including the new controversial X(3872) and the structure found recently by Belle around 3875MeV in the hidden charm sector. Also new resonances are predicted, some of them with exotic quantum numbers.