118420845
Parton-distribution functions for the pion and kaon in the gauge-invariant nonlocal chiral-quark model
chiral action from the nonlocal chiral-quark model, resulting in that the vector currents are conserved. All the model parameters are determined phenomenologically with the normalization condition for PDF and the empirical values for the pseudoscalar-meson weak-decay constants. We consider the momentum dependence of the eective quark mass properly within the model calculations. It turns out that the leading local contribution provides about 70% of the total strength for PDF, whereas the nonlocal one that is newly taken into account in this work for the gauge invariance does the rest. High-Q 2 evolution to 27 GeV 2 is performed for valance-quark distribution function (VQDF), using the DGALP equation. The moments for the pion and kaon VQDFs are also computed. The numerical results are compared with the empirical data and theoretical estimations, and show qualitatively agreement with them.
117519861
Lambda(1405) photoprodcution with p-wave contributions
In this report, we present our recent studies on the Lambda(1405,1/2-)=Lambda* photoproduction via the gamma p -> K+ pi Sigma scattering process, employing a coupled-channel formalism, i.e., the chiral unitary model, which respects chiral dynamics in terms of the Weinberg-Tomozawa meson baryon interaction. In addition to the dynamically generated s-wave resonance, Lambda*, we include the p-wave resonance contribution from Sigma(1385,3/2+). We observe that the p-wave contribution provides considerable effects on the pi-Sigma invariant-mass spectrum. It also turns out that, within the present level of calculations, we can reproduce hardly the recent Lambda* photoproduction experiment by LEPS collaboration at SPring-8.
118435680
Unpolarized Fragmentation Function for the Pion and Kaon via the Nonlocal Chiral-Quark Model
In this talk we present our recent studies for the unpolarized fragmentation functions for the pion and kaon, employing the nonlocal chiral quark model, which manifests the nonlocal interaction between the quarks and pseudoscalar mesons, in the light-cone frame. It turns out that the nonlocal interaction produces considerable differences in comparison to typical local-interaction models.
118442034
Electrical conductivity of quark matter at finiteTunder external magnetic field
We investigate the electrical conductivity (sigma) of quark matter via the Kubo formula at finite temperature and zero quark density (T>0, mu=0) in the presence of an external strong magnetic field. For this purpose, we employ the dilute instanton-liquid model, taking into account its temperature modification with the trivial-holonomy caloron distribution. By doing that, the momentum and temperature dependences for the effective quark mass and model renormalization scale are carefully evaluated. From the numerical results, it turns out that sigma\approx(0.02 ~ 0.15)/fm for T=(0 ~ 400) MeV with the relaxation time tau=(0.3 ~ 0.9) fm. In addition, we also parameterize the electrical conductivity as sigma/T ~ (0.46,0.77,1.08,1.39)C_EM for tau=(0.3,0.5,0.7,0.9) fm, respectively. These results are well compatible with other theoretical estimations, including those from the lattice QCD simulations. It also turns out that the external magnetic field plays only a minor role for sigma even for the very strong one B_0 ~ m^2_pi*10 and becomes relatively effective for T\lesssim200 MeV. Moreover, we compute the soft photon emission rate from the quark-gluon plasma, using the electrical conductivity calculated.
118833296
Photoproduction of K* meson off the proton target with the Regge contributions
We investigate the K*Λ(1116) photoproduction off the proton target by employing the treelevel Born approximation within the effective Lagrangian approach. We take into account the κ, K, and K* exchanges in the t channel in addition to the ground-state nucleon- and hyperon-pole contributions in the s and the u channels with the gauge-invariant form-factor scheme. The nucleon and the hyperon resonances, D13(2080) and Σ*(1385), are also included. We take into account the Regge trajectories of the strange mesons for the t-channel contributions in such a way that the Feynman and Regge propagators are interpolated smoothly for the relevant photon energy region. We provide numerical results for the differential cross sections, which result in qualitatively good agreement with the presently available experimental data from the CLAS collaboration at Jefferson laboratory. The Feynman-Regge interpolation for the meson exchanges turns out to play a critical role in reproducing the data simultaneously for the low and the relatively high energy regions. We also compute the total cross sections, momentum-transfer dependence of the differential cross sections in the t-channel, and the photon-beam asymmetry as useful guides for future experiments.
118457760
Charged pion photoproduction with the Delta(1232) baryon beyond the resonance region
We investigate the charged pion photoproduction off the proton target with the {Delta}(1232) baryon, i.e., {gamma}p{yields}{pi}{sup -{Delta}++}(1232) and {gamma}p{yields}{pi}{sup +{Delta}0}(1232), based on the effective Lagrangian method, beyond the resonance region, {radical}(s) > or approx. 2 GeV. We employ the {pi}- and {rho}-meson Regge trajectories in the t channel, in addition to the proton and {Delta} pole, in the s and u channels, respectively, and the contact-interaction contributions. A specific scheme for the form factor which satisfies the Ward-Takahashi identity, crossing symmetry, and on-shell condition is taken into account. We also consider a smooth interpolation between the Regge and Feynman propagators for the t-channel meson exchanges as a function of the Mandelstam variable s. We present the numerical results for the energy and angular dependences of the cross sections and the double- and single-polarization observables. It turns out that the present framework reproduces the experimental data qualitatively very well. In particular, the interpolation between the two propagators plays a crucial role in reproducing the high-energy experimental data correctly. The {pi}{sup +} decay-angle distribution is also studied using the {Delta}{sup ++}-decay frame, i.e., the Gottfried-Jackson frame. The present results will be a useful guide for future high-energy photon-beam experiments.
51688538
Properties of holographic mesons on dense medium
A bstractWe study the energy dispersions of holographic light mesons and their decay constants on dense nuclear medium. As the spatial momenta of mesons along the boundary direction increase, both observables of the mesons not only increase but also split according to the isospin charges. The decay constant of the negative meson is more large than that of the positive meson of the same type due to the chemical potentials of the background nucleons.