The renormalon contribution to the current product j μ5 j S

The product of an axialvector and a scalar current and its relation to the chiral-odd distribution function h ₁ is discussed in the framework of the renormalon approach. Using a bag-model calculation for h ₁, we calculate its intrinsic uncertainty due to renormalon poles. The result is given as a function of Bjorken-x as well as for the first moments separately. Received: 9 November 1998 / Revised version: 22 January 1999     

Chiral Invariant Phase Space model

The CHIPS (CHiral Invariant Phase Space) model is used for approximation of the Drell-Yan process in hadron-nucleon interactions. It is proved that the Drell-Yan cross-section at low p _T ² is a function of only x₁ and x₂ and does not evolve as a function of the squared mass of the lepton pair M². The CHIPS model predicts that the Drell-Yan structure functions evolve as a function of p _T ² . This p _T ² evolution can be measured in experiments at RHIC and LHC.     

Radiative transitions in mesons in a non-relativistic quark model

In the framework of the non-relativistic quark model, an exhaustive study of radiative transitions in mesons is performed. Emphasis is placed on several points. Some traditional approximations (long-wavelength limit, non-relativistic phase space, dipole approximation for E1 transitions, Gaussian wave functions) are analyzed and their effects commented. A complete treatment using three different types of realistic quark-antiquark potential is made. The overall agreement with experimental data is quite good, but some improvements are suggested. Received: 16 October 2001 / Accepted: 18 December 2001     

Prompt contributions to the dilepton yield in heavy ion collisions

The mass spectrum is calculated for those dileptons which are produced in the early phase of a heavy ion collisions via the direct production NN → l⁺l⁻X and via the Compton process GN → l⁺l⁻X with prompt gluons radiated in preceding NN interactions. Both mechanisms produce a mass spectrum which decreases steeply with invariant mass of the l⁺l⁻ pair and which is below the CERES data for Pb-Au collisions by about one order of magnitude. Received: 1 December 1999 / Revised version: 18 February 2000     

Decay rates of quarkonia with NRQCD formalism using spectroscopic parameters of potential models

Decay rates of quarkonia are studied within the framework of NRQCD formalism. The basic parameters of the formalism have been obtained from different potential schemes studied for the spectra of quarkonia. We estimate the heavy-quarkonia mass spectra, radiative and leptonic widths and compare them with other contemporary theoretical approaches and experimental results.     

Single heavy flavour baryons using Coulomb plus a power law interquark potential

Properties of single heavy flavor baryons in a non-relativistic potential model with colour Coulomb plus a power law confinement potential have been studied using a simple variational method. The ground-state masses of single heavy baryons and the mass difference between the J ^P = ⁺ and J ^P = ⁺ states are computed using a spin-dependent two-body potential. Using the spin-flavour structure of the constituting quarks and by defining an effective confined mass of the constituent quarks within the baryons, the magnetic moments are computed. The masses and magnetic moments of the single heavy baryons are found to be in accordance with the existing experimental values and with other theoretical predictions. It is found that an additional attractive interaction of the order of -200 MeV is required for the antisymmetric states of (Q c, b) . It is also found that the spin-hyperfine interaction parameters play a decisive role in hadron spectroscopy.     

Towards an understanding of heavy baryon spectroscopy

The recent observation at CDF and D0 of Σ _b , Σ _b ^* and Ξ _b baryons opens the door to the advent of new states in the bottom baryon sector. The states measured provide sufficient constraints to fix the parameters of phenomenological models. One may therefore consistently predict the full bottom baryon spectra. For this purpose we have solved exactly the three-quark problem by means of the Faddeev method in momentum space. We consider our guidance may help experimentalists in the search for new bottom baryons and their findings will help in constraining further the phenomenological models. We identify particular states whose masses may allow to discriminate between the dynamics for the light quark pairs predicted by different phenomenological models. Within the same framework we also present results for charmed, doubly charmed, and doubly bottom baryons. Our results provide a restricted possible assignment of quantum numbers to recently reported charmed-baryon states. Some of them are perfectly described by D-wave excitations with J ^P = 5/2⁺, as the Λ _c (2880), Λ _c (3055), and Λ _c (3123). Communicated by V. Vento     

Gluelump model with transverse constituent gluons

We show that C -odd gluelumps can be successfully described as bound states of a single transverse constituent gluon evolving in the flux-tube-like potential generated by a static color-octet source. The use of a helicity degree of freedom rather than a spin one for the constituent gluon forbids the states that are not observed in lattice QCD. Our model leads to a gluelump mass spectrum in remarkable agreement with the available lattice data provided that an additional parity splitting mass term is introduced. We argue that such a term is due to instanton-induced interactions in gluelumps.     

Initial-state nuclear effects in proton-nucleus collisions

Two important initial-state nuclear effects in hadron-nucleus collisions are considered. The ratios of inclusive differential cross-sections for Drell-Yan dimuon production are calculated. The calculated results are compared to the E866 data. It is shown that the consideration of multiple soft rescatterings of incident quarks in nuclei and initial-state quark energy loss effects allow to get a good agreement between the calculated results and the experimental data.     

On the cross-section peaks for a heavy-quark bound state

We discuss the values of resonance peaks of the cross section of a heavy-quark bound state obtained by means of a Green function method applied to a Coulombic model and compare the result to the ϒ and J/ψ data.     

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments. Received: 10 March 1999 / Revised version: 14 June 1999     

Heavy quarkonia from classical SU(3) Yang-Mills configurations

A generalized Cho-Faddeev-Niemi ansatz for SU(3) Yang-Mills is investigated. The corresponding classical field equations are solved for its simplest parametrization. From these solutions it is possible to define a confining non-relativistic central potential used to study heavy quarkonia. The associated spectra reproduces the experimental spectra with an error of less than 3% for charmonium and 1% for bottomonium. Moreover, the recently discovered new charmonium states can be accomodate in the spectra, keeping the same level of precision. The leptonic widths show good agreement with the recent measurements. The charmonium and bottomonium E1 electromagnetic transitions widths are computed and compared with the experimental values.     

Nucleon form factors in a simple three-body quark model

We construct a simple 3-body quark model for the non strange nucleon resonances and we give results for the spectrum, the helicity amplitudes and the transition form factors. All the observables, in particular the transition form factors, are evaluated analytically and the results are compared with those of other models. Received: 15 November 1997     

The radiative decay ϕ → γππ in a coupled-channel model and the structure of f0(980)

A coupled-channel model is used to study the nature of the scalar mesons produced in the decay ϕ → γππ. The K molecular picture of f₀(980) is found to be in a good agreement with the recent experimental data from SND and CMD-2. The structure of the light scalar mesons is elucidated by investigating the S-matrix poles and the q spectral density.     

Roper resonances in chiral quark models

We derive a method to calculate the multi-channel K -matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data is achieved if in addition to the elastic channel we include the and N ( channels where the -meson models the correlated two-pion decay. We solve the integral equation for the K -matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the (1232) and the N(1440) resonances compared to the bare quark values.     

The small axial charge of the N(1535)-resonance

There is a natural cancellation between the contributions of the qqq and qqqq components to the axial charge of the N(1535)-resonance. While the probability of the former is larger than that of the latter, its coefficient in the axial charge expression is exceptionally small. The magnitude of two of the corresponding coefficients of the qqqq components is in contrast large and has the opposite sign. This result provides a phenomenological illustration of the recent unquenched lattice calculation result that the axial charge of the N(1535)-resonance is very small, if not vanishing (T.T. Takahashi, T. Kunihiro, arXiv: 0801.4707 [hep-lat]). The result sets an upper limit on the magnitude of the probability of qqqq components as well.     

An improved approximation scheme for the centrifugal term and the Hulthén potential

We present a new approximation scheme for the centrifugal term to solve the Schrödinger equation with the Hulthén potential for any arbitrary l -state by means of a mathematical Nikiforov-Uvarov (NU) method. We obtain the bound-state energy eigenvalues and the normalized corresponding eigenfunctions expressed in terms of the Jacobi polynomials or hypergeometric functions for a particle exposed to this potential field. Our numerical results of the energy eigenvalues are found to be in high agreement with those results obtained by using the program based on a numerical integration procedure. The s -wave (l = 0analytic solution for the binding energies and eigenfunctions of a particle are also calculated. The physical meaning of the approximate analytical solution is discussed. The present approximation scheme is systematic and accurate.     

Screened potential and quarkonia properties at high temperatures

We perform a quark model calculation of the quarkonia b and c spectra using smooth and sudden string breaking potentials. The screening parameter is scale dependent and can be related to an effective running gluon mass that has a finite infrared fixed point. A temperature dependence for the screening mass is motivated by lattice QCD simulations at finite temperature. Qualitatively different results are obtained for quarkonia properties close to a critical value of the deconfining temperature when a smooth or a sudden string breaking potential is used. In particular, with a sudden string breaking potential quarkonia radii remain almost independent of the temperature up to the critical point, only well above the critical point the radii increase significantly. Such a behavior will impact the phenomenology of quarkonia interactions in medium, in particular for scattering dissociation processes.     

Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

We evaluate static properties and semileptonic decays for the ground state of doubly heavy Ξ, Ξ', Ξ ^* and Ω, Ω', Ω ^* baryons. Working in the framework of a nonrelativistic quark model, we solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one-gluon exchange. Our results for static properties (masses, charge radii and magnetic moments) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy Ξ, Ξ'(J = 1/2) and Ω, Ω'(J = 1/2) baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark-diquark approximation. An erratum to this article is available at .