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

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 $K$-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

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

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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