H. Matsufuru

Charmonium at finite temperature in quenched lattice QCD

We study charmonium correlators in pseudoscalar and vector channels at finite temperature using lattice QCD simulation in the quenched approximation. Anisotropic lattices are used in order to have sufficient numbers of degrees of freedom in the Euclidean temporal direction. We focus on the low energy structure of the spectral function, corresponding to the ground state in the hadron phase, by applying the smearing technique to enhance the contribution to the correlator from this region. We employ two analysis procedures: the maximum entropy method (MEM) for the extraction of the spectral function without assuming a specific form, to estimate the shape of the spectral function, and the standard χ2 fit analysis using typical forms in accordance with the result of MEM, for a more quantitative evaluation. To verify the applicability of the procedures, we first analyze the smeared correlators as well as the point correlators at zero temperature. We find that by shortening the t-interval used for the analysis (a situation inevitable at T>0) the reliability of MEM for point correlators is lost, while it subsists for smeared correlators. Then the smeared correlators at T≃ 0.9 Tc and 1.1 Tc are analyzed. At T≃ 0.9 Tc, the spectral function exhibits a strong peak, well approximated by a delta function corresponding to the ground state with almost the same mass as at T=0. At T≃ 1.1 Tc, we find that the strong peak structure still persists at almost the same place as below Tc, but with a finite width of a few hundred MeV. This result indicates that the correlators possess a nontrivial structure even in the deconfined phase. PACS: 12.38.Gc Lattice QCD calculations – 12.38.Mh Quark-gluon plasma

Three-Quark Potential in SU(3) Lattice QCD

The static three-quark ( 3Q) potential is studied in SU(3) lattice QCD with 12(3)x24 and beta = 5.7 at the quenched level. From the 3Q Wilson loop, 3Q ground-state potential V(3Q) is extracted using the smearing technique for ground-state enhancement. With accuracy better than a few percent, V(3Q) is well described by a sum of a constant, the two-body Coulomb term, and the three-body linear confinement term sigma(3Q)L(min), with L(min) the minimal value of total length of color flux tubes linking the three quarks. Comparing with the Q-&Qmacr; potential, we find a universal feature of the string tension, sigma(3Q) approximately sigma(Q&Qmacr;), and the OGE result for Coulomb coefficients, A(3Q) approximately 1 / 2A(Q&Qmacr;).

Renormalization group flow of SU(3) lattice gauge theory : Numerical studies in a two coupling space

We investigate the renormalization group (RG) flow of SU(3) lattice gauge theory in a two coupling space with couplings β11 and β12 corresponding to 1×1 and 1×2 loops, respectively. Extensive numerical calculations of the RG flow are made in the fourth quadrant of this coupling space, i.e., β11>0 and β12<0 . Swendsens factor two blocking and the Schwinger–Dyson method are used to find an effective action for the blocked gauge field. The resulting renormalization group flow runs quickly towards an attractive stream which has an approximate line shape. This is a numerical evidence of a renormalized trajectory which locates close to the two coupling space. A model flow equation which incorporates a marginal coupling (asymptotic scaling term), an irrelevant coupling and a non-perturbative attraction towards the strong coupling limit reproduces qualitatively the observed features. We further examine the scaling properties of an action which is closer to the attractive stream than the currently used improved actions. It is found that this action shows excellent restoration of rotational symmetry even for coarse lattices with a∼0.3 fm.

Meson correlators in finite temperature lattice QCD

We analyze temporal and spatial meson correlators in quenched lattice QCD at T>0. Below Tc we observe little change in the meson properties as compared with T50. Above Tc we observe new features: chiral symmetry restoration and signals of plasma formation, but also an indication of persisting ‘‘mesonic’’ ~metastable! states and different temporal and spatial ‘‘masses’’ in the mesonic channels. This suggests a complex picture of QGP in the region (1 ‐1.5)Tc .

Glueball properties at finite temperature in SU(3) anisotropic lattice QCD

The thermal properties of the glueballs are studied using SU(3) anisotropic lattice QCD with beta=6.25, the renormalized anisotropy xi=a_s/a_t=4 over the lattice of the size 20^3times N_t with N_t = 24, 26, 28, 30, 33, 34, 35, 36, 37, 38, 40, 43, 45, 50, 72 at the quenched level. To construct a suitable operator on the lattice, we adopt the smearing method, and consider its physical meaning in terms of the operator size. First, we construct the temporal correlators G(t) for the 0^{++} and 2^{++} glueballs, using more than 5,000 gauge configurations at each temperature. We then measure the pole-mass of the thermal glueballs from G(t). For the lowest 0^{++} glueball, we observe a significant pole-mass reduction of about 300 MeV near T_c or m_G(Tsimeq T_c) simeq 0.8 m_G(Tsim 0), while its size remains almost unchanged as rho(T) simeq 0.4fm. Finally, for completeness, as an attempt to take into account the effect of thermal width Gamma(T) at finite temperature, we perform a more general new analysis of G(t) based on its spectral representation. By adopting the Breit-Wigner form for the spectral function rho(omega), we perform the best-fit analysis as a straightforward extension to the standard pole-mass analysis. The result indicates a significant broadening of the peak as Gamma(T) sim 300 MeV as well as rather modest reduction of the peak center of about 100 MeV near T_c for the lowest 0^{++} glueball. The temporal correlators of the color-singlet modes corresponding to these glueballs above T_c are also investigated.

Numerical study of O ( a ) improved Wilson quark action on an anisotropic lattice

The

Negative parity baryons in quenched anisotropic lattice QCD

O(a)

Chiral properties of light mesons with

improved Wilson quark action on the anisotropic lattice is investigated. We carry out numerical simulations in the quenched approximation at three values of lattice spacing (

N_f=2+1

a_{sigma}^{-1}=1

overlap fermions

--2 GeV) with the anisotropy