531 research outputs found

    Studies on the polarization transfer coefficients C_x and C_z in the gamma p -> K^+ Lambda(1520,3/2^-) reaction process

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    We investigate the polarization transfer coefficients C_(x,z) for the gamma p -> K^+ Lambda(1520,3/2^-) reaction process, in which the photon is polarized circularly and the Lambda(1520,3/2^-) along the x- or z-axis. To this end, we employ the effective Lagrangian method at tree level and the gauge-invariant form factor scheme. In addition to the Born terms, (s,u,t_K,t_K^*)-channels and contact term, we include the nucleon resonance D_{13}(2080) in the s-channel. We compute the C_(x,z) as functions of theta_K as well as E_cm. It turns out that the K^*-exchange and D_{13} contributions are negligible within available experimental and theoretical inputs for them. In contrast, we observe that the contact and K-exchange contributions play dominant roles for determining the C_(x,z). Especially, the KK-exchange enhances the transverse polarization transfer C_x considerably.Comment: 11 pages, 13 figure

    An effective thermodynamic potential from the instanton vacuum with the Polyakov loop

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    In this talk, we report our recent studies on an effective thermodynamic potential (Omega_eff) at finite temperature (T>0) and zero quark-chemical potential (mu_R=0), using the singular-gauge instanton solution and Matsubara formula for N_c=3 and N_f=2 in the chiral limit, i.e. m_q=0. The momentum-dependent constituent-quark mass is computed as a function of T, together with the Harrington-Shepard caloron solution in the large-N_c limit. In addition, we take into account the imaginary quark-chemical potential mu_I = A_4, indentified as the traced Polayakov-loop (Phi) as an order parameter for the Z(N_c) symmetry, characterizing the confinement (intact) and deconfinement (spontaneously broken) phases. As a consequence, we observe the crossover of the chiral (chi) order parameter sigma^2 and Phi. It also turns out that the critical temperature for the deconfinement phase transition, T^Z_c is lowered by about (5~10) % in comparison to the case with the constant constituent-quark mass. This behavior can be understood by considerable effects from the partial chiral restoration and nontrivial QCD vacuum on the Phi. Numerical results show that the crossover transitions occur at (T^chi_c,T^Z_c) ~ (216,227) MeV.Comment: 10 pages, 5 figures, Talk given at the international workshop Hadron Nuclear Physics (HNP) 2011, 21~24 Feb 2011, Pohang, Kore

    Scalar susceptibility from the instanton vacuum with meson-loop corrections

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    The scalar susceptibility (chi_s) of QCD, which represents the response of the chiral condensate to a small perturbation of explicit chiral-symmetry breaking, is investigated within the nonlocal chiral quark model (NLchiQM) based on the instanton vacuum configuration for N_f = 2. We also take into account 1/N_c meson-loop (ML) corrections including scalar and pseudoscalar mesons. It turns out that the chiral condensate is modified to a large extend by the ML corrections in the vicinity of m = 0, whereas its effect becomes weak beyond m ~ 100 MeV. As numerical results, we find that chi_s = -0.34 GeV^2 with the ML corrections and 0.18 GeV^2 without it, respectively. From these observations, we conclude that the ML corrections play an important role in the presence of finite current-quark mass.Comment: 11 pages, 3 figures, accepted for publication in Phys.Rev.
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