119116975
Quark–gluon mixed condensate for the SU(2) light-flavor sector at finite temperature
Abstract We investigate the quark–gluon mixed condensate 〈 q ¯ σ ⋅ G q 〉 ≡ m 0 2 〈 q ¯ q 〉 for the SU ( 2 ) light-flavor sector at finite temperature ( T ). Relevant model parameters, such as the average (anti)instanton size, inter-(anti)instanton distance, and constituent-quark mass at zero virtuality, are modified as functions of T , employing the trivial-holonomy caloron solution. By doing that, we observe correct chiral restoration patterns depending on the current-quark mass m , i.e. the second-order and crossover chiral phase transitions for the zero and finite current-quark masses, respectively. We also perform the two-loop renormalization-group (RG) evolution for the both condensates by increasing the renormalization scale μ = ( 0.6 → 2.0 ) GeV . It turns out that the mixed condensate is insensitive to the RG evolution, whereas the quark condensate become larger considerably by the evolution. Numerically, we obtain − 〈 q ¯ σ ⋅ G q 〉 1 / 5 = ( 0.45 – 0.46 ) GeV at T = 0 within the present theoretical framework, and the mixed condensate plays the role of the chiral order parameter for finite T . The ratio of the two condensates m 0 2 is almost flat below the chiral transition T ( T 0 ), and increases rapidly beyond it. From a simple linear parametrization, we obtain m 0 2 ( T ) / m 0 2 ( 0 ) ≈ ( 0.07 , 0.47 ) T / T 0 + ( 1 , 0.6 ) for ( T ≲ T 0 , T ≳ T 0 ) at μ = 0.6 GeV . The present results are compared with other theoretical ones including the lattice QCD simulations, and show qualitatively good agreement with them.
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.
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.
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.
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.
119190584
Chiral magnetic effect at low temperature
We investigate the chiral magnetic effect (CME) under a strong magnetic field B = B 0 x 3 at low temperature T ≲ T χ c . For this purpose, we employ the instanton vacuum configuration with the finite instanton-number fluctuation Δ, which relates to the nontrivial topological charge Q t . We compute the vacuum expectation values of the local chiral density 〈ρ χ 〉, chiral charge density 〈n χ 〉, and induced electromagnetic current 〈j μ 〉, which signal the CME, as functions of T and B o . We observed that the longitudinal electromagnetic current is much larger than the transverse one, |j ⊥ /j ∥ | ∼ Q t , and 〈n χ 〉 is equal to |〈j 3,4 〉|. It also turns out that the CME becomes insensitive to the magnetic field as T increases, since the instanton effect decreases. Within our framework, the instanton contribution to the CME becomes almost negligible beyond T ≈ 300 MeV.
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.