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.
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.
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.
119249308
Chiral restoration at finite T under the magnetic field with the meson-loop corrections
We investigate the (partial) chiral restoration at finite temperature (T) under the strong external magnetic field B=B{sub 0}z-circumflex of the SU(2) light-flavor QCD matter. To this end, we employ the instanton-liquid QCD vacuum configuration accompanied with the linear Schwinger method for inducing the magnetic field. The Harrington-Shepard caloron solution is used to modify the instanton parameters, i.e. the average instanton size ({rho}) and interinstanton distance (R), as functions of T. In addition, we include the meson-loop corrections as the large-N{sub c} corrections because they are critical for reproducing the universal chiral-restoration pattern. We present the numerical results for the constituent-quark mass as well as chiral condensate, which signal the spontaneous breakdown of chiral-symmetry (SB{chi}S), as functions of T and B{sub 0}. From our results we observe that the strengths of those chiral order parameters are enhanced with respect to B{sub 0} due to the magnetic-catalysis effect. We also find that there appears a region where the u and d-quark constituent masses coincide with each other at eB{sub 0{approx_equal}}(7-9)m{sub {pi}}{sup 2}, even in the presence of the explicit isospin breaking (m{sub u{ne}}m{sub d}). The critical T for the chiral restoration T{sub c} tends to shift to the higher temperature in themore » presence of the B{sub 0} for the chiral limit but keeps almost stationary for the physical quark mass case. The strength of the isospin breaking between the quark condensates is also explored in detail by defining the ratio R{identical_to}( - )/( + ), which indicates the competition between the explicitly isospin-breaking effect and magnetic-catalysis effect. We also compute the pion weak-decay constant F{sub {pi}} and pion mass m{sub {pi}} below T{sub c}, varying the strength of the magnetic field, showing correct partial chiral-restoration behaviors. Besides we find that the changes for the F{sub {pi}} and m{sub {pi}} due to the magnetic field is relatively small, in comparison to those caused by the finite T effect.« less
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.