Heavy-light mesons in a relativistic model

We study the heavy-light mesons in a relativistic model, which is derived from the Bethe-Salpeter equation by applying the Foldy-Wouthuysen transformation to the heavy quark. The kernel we choose is based on scalar confinement and vector Coulomb potentials. The transverse interaction of the gluon exchange is also taken into account in this model. The spectra and wave functions of D, D_s, B, B_s meson states are obtained. The spectra are calculated up to the order of 1/m Q, and wave functions are treated to leading order.     

Mass Spectrum and Decay Properties of D Meson

A comparative study of the spectroscopy and decay properties of the D meson is carried out within the framework of phenomenological quark-antiquark potential (Coulomb plus power) model using hydrogenic and Gaussian wave function. The spin-hyperfine, spin-orbit and tensor interactions are employed to obtain the pseudoscalar and vector meson masses incorporating the effect of mixing. The decay constants (f _P/V ) are computed with QCD correction using the wave function at the origin. The leptonic branching fractions and electromagnetic transition rates are also calculated in this scheme. Our predictions at potential index ν=1 are in good agreement with experimental results as well as lattice and other theoretical models.     

Perturbative QCD study on the photonic penguin contributions to the decay B\rightarrow K^* \gamma

Including corrections of order , we present an analysis of photonic penguin contributions to the decay in the perturbative QCD framework. Employing several models of the meson wave functions, we demonstrate that the corrections of are enhanced and will provide substantial contributions to the decay because of the meson wave function being sharply peaked (bound state effect). The numerical predictions for the corrections are about which depend on the non-perturbative inputs such as the meson wave functions and the -quark mass. Received: 8 July 1997 / Published online: 23 February 1998     

Coulomb Deexcitation and Non-Resonant Meson Transfer from Excited States of Mesic Hydrogen Isotope Atoms

Advanced adiabatic approach is used to calculate the rates of the Coulomb deexcitation and charge transfer processes including meson transfer from a heavy isotope to a light one.     

An improved covariant treatment of the light mesons

In an earlier paper a covariant version of the two-particle Dirac equation-employing a potential which was a function of the (invariant) proper separation-was used to fit the light meson quark-anti-quark bound states. This paper improves upon that work by introducing a better separation of the equation into internal and external coordinates, and a better separation into angular and radial coordinates. The new eigenvalue which arises from the introduction of hyperspherical harmonics is related to the meson energy in a more rigorous manner than before. As a result, the light meson trajectories can be better fit with fewer free parameters. In particular, the potential now has only Coulomb and linear terms, with no constant term, and current masses are used for the quarks rather than constituent masses. The reduction of the equation to Schrödinger form is discussed. It is shown how the non-relativistic reduction of the linear potential can lead to a constant term in the Schrödinger equation potential, as well as an enhancement of the Coulomb term. The resulting non-relativistic potential is similar to potentials used in successful fits of the charmonium spectrum.     

Light 0- Meson Solution of Bethe-Salpeter Equation Involving the Vacuum Condensates in QCD

We dkcuss the Bethe-Salpeter equation involving the vacuum condensates in QCD in the backgrouud fields. The bound state equation for the light 0^- meson (π and K) is solved in the ladder approximation of single gluon exchange, where the gluon propagator is calculated in tree level of a gluon condensate and a quark condensate. The kernel is divided into two parts: perturbative and non-pert,urbative. The non-perturbative part is determined by the vacuum condensate. Pseudo-scalar meson spectrum and decay constants are in good agreement with data.     

Meson and tetra-quark mixing

The mixing between qq̄ meson and qq̄qq̄ tetra-quark states is examined within an effective QCD Coulomb gauge Hamiltonian model. Mixing matrix elements of the Hamiltonian are computed and then diagonalized yielding an improved prediction for the low-lying J^PC=0^±+,1^– isoscalar spectra. Mixing effects were found significant for the scalar hadrons but not for the 1^– states, which is consistent with the ideal mixing of vector mesons. A perturbative assessment of the exact QCD kernel is also reported. PACS  12.39.Mk; 12.39.Pn; 12.39.Ki; 12.40.Yx     

Charge symmetry breaking interactions and coulomb energy differences

A detailed study of the possibility that the long standing discrepancies between theory and experiment in the values of Coulomb displacement energies have their origin in the charge asymmetry of the nuclear force is presented. A review of the present status of the theory of Coulomb displacement energies of mirror states is given. We have constructed a phenomenological charge asymmetric potential that can remove the Coulomb energy discrepancies for several mirror nuclei yet having only minimal effect on the ¹S₀ nucleon-nucleon scattering length. The form of this potential is however not compatible with the contributions due to charge asymmetric meson exchange processes that have been considered in the literature. We assume that these meson exchange effects can be reasonably described, up to strength factors, by a sum of one-pion, one-scalar-meson (σ) and one-vector-meson exchange potentials. The need for some additional type of charge asymmetric effect, e.g. three-body forces, is pointed out.     

Charmed hadron production in \pi p and Kp collisions and leading particle effect by constituent quark-diquark cascade model

We investigate the meson, baryon and anti-baryon productions in and collisions in terms of a constituent cascade model which includes charm flavour. The constituent diquark in an incident baryon has a tendency to get a large momentum fraction, resulting in considerable difference of subenergies for particle productions from quark-diquark and quark-antiquark chains in a meson-baryon collision. As a consequence, the leading particle effects on meson productions are expected to be quite different in and beams at present accelerator energies. Received: 5 November 1996 / Revised version: 30 June 1997 / Published online: 20 February 1998     

Excited state mass spectra,decay properties and Regge trajectories of charm and charm-strange mesons

The framework of a phenomenological quark-antiquark potential(Coulomb plus linear confinement)model with a Gaussian wave function is used for detailed study of masses of the ground, orbitally and radially excited states of heavy-light Qq,(Q=c,q=u/d,s) mesons. We incorporate a O(1/m) correction to the potential energy term and relativistic corrections to the kinetic energy term of the Hamiltonian. The spin-hyperfine, spin-orbit and tensor interactions incorporating the effect of mixing are employed to obtain the pseudoscalar, vector, radially and orbitally excited state meson masses. The Regge trajectories in the(J,M~2) and(nr,M~2) planes for heavy-light mesons are investigated with their corresponding parameters. Leptonic and radiative leptonic decay widths and corresponding branching ratios are computed. The mixing parameters are also estimated. Our predictions are in good agreement with experimental results as well as lattice and other theoretical models.     

The linear meson model and chiral perturbation theory

We compare the linear meson model and chiral perturbation theory in next to leading order in the quark mass expansion. In particular, we compute the couplings – of chiral perturbation theory as functions of the parameters of the linear model. They are induced by the exchange of scalar mesons. We use a phenomenological analysis of the effective vertices of the linear model in terms of pseudoscalar meson masses and decay constants. Our results for the agree with previous phenomenological estimates. Received: 21 April 1997 / Published online: 20 February 1998     

Interpolating between soft and hard dynamics in deep inelastic scattering

An explicit model for the proton structure function is suggested, interpolating between low- vector meson dominance and Regge behavior, on the one hand, and the high- solution of the Gribov-Lipatov-Altarelli-Parisi evolution equation, on the other hand. The model is fitted to the experimental data in a wide range of the kinematical variables with emphasis on the low-x HERA data. The boundaries, transition region and interface between various regimes are quantified. Received: 9 March 1998 / Revised version: 26 May 1998 / Published online: 5 October 1998     

Model independent constraints from vacuum and in-medium QCD Sum Rules

We discuss QCD sum rule constraints based on moments of vector meson spectral distributions in the vacuum and in a nuclear medium. Sum rules for the two lowest moments of these spectral distributions do not suffer from uncertainties related to QCD condensates of dimension higher than four. We exemplify these relations for the case of the ω meson and discuss the issue of in-medium mass shifts from this viewpoint. Received: 22 December 1998 / Revised version: 13 January 1999     

Resolving the Bethe–Salpeter Kernel

A novel method for constructing a kernel for the meson bound-state problem is described.It produces a closed form that is symmetry-consistent(discrete and continuous) with the gap equation defined by any admissible gluon-quark vertex,Γ.Applicable even when the diagrammatic content of Γ is unknown,the scheme can foster new synergies between continuum and lattice approaches to strong interactions.The framework is illustrated by showing that the presence of a dressed-quark anomalous magnetic moment in Γ,an emergent feature of strong interactions,can remedy many defects of widely used meson bound-state kernels,including the mass splittings between vector and axial-vector mesons and the level ordering of pseudoscalar and vector meson radial excitations.     

Low energy theorems in a nonlocal chiral quark model at finite temperature

We solve the Dyson equation and the Bethe-Salpeter equation for a nonlocal effective quark interaction kernel which is instantaneous and separable. The momentum-dependent dynamical quark mass, the scalar and pseudoscalar meson masses, the pion decay constant and the quark meson coupling constant are calculated at finite temperature in the Hartree approximation for the quark self energy. We obtain relations between these quantities, which coincide to leading order in the current quark mass (m ₀/Δm) with the basic low energy theorems: the Goldstone theorem, the Gell-Mann-Oakes-Renner relation and the Goldberger-Treimann relation at finite temperature. A formula for the σ?π mass gap is obtained which exhibits an additional contribution from the momentum dependence of the quark mass.     

Two–loop integrals in chiral perturbation theory

We consider chiral perturbation theory in the meson sector at order . In the terminology of the external field technique, the genuine two–loop diagrams so generated are of the sunset type. We discuss the evaluation of several of these in the case where the masses of the particles running in the loops are equal. In particular, we present integral representations that are suitable for the evaluation of diagrams in kinematical regions where branch points and cuts are present. Received: 14 April 1998 / Published online: 7 August 1998