Y. Tago

Scaling study of pure gauge lattice QCD by Monte Carlo renormalization group method

The scaling behavior of pure gauge SU(3) in the region [beta]=5.85[minus]7.60 is examined by a Monte Carlo renormalization group analysis. The coupling shifts induced by factor 2 blocking are measured on both 32[sup 4] and 16[sup 4] lattices with high statistics. A systematic deviation from naive 2-loop scaling is clearly seen. The mean field and effective coupling constant schemes explain part, but not all, of the deviation. It can be accounted for by a suitable change of coupling constant, including a correction term [ital O]([ital g][sup 7]) in the 2-loop lattice [beta] function. Based on this improvement, [radical][sigma] /[Lambda][sub M[bar S]][sup [ital n]][sub [ital f]]=0 is estimated to be 2.2[plus minus]0.1 from the analysis of the string tension [sigma].

Search for effective lattice action of pure QCD

We study a coupling flow of pure QCD gauge system by using the Monte Carlo Renormalization Group method. A rough location of the renormalized trajectory in two coupling space is obtained. Also we compare 4 different actions; (a)standard Wilson, (b)Symanziks, (c)Iwasakis and (d)QCDTAROs. The rotational symmetry is restored better as an action gets close to the renormalized trajectory.Abstract We study a coupling flow of pure QCD gauge system by using the Monte Carlo Renormalization Group method. A rough location of the renormalized trajectory in two coupling space is obtained. Also we compare 4 different actions; (a)standard Wilson, (b)Symanziks, (c)Iwasakis and (d)QCDTAROs. The rotational symmetry is restored better as an action gets close to the renormalized trajectory.

Finite temperature gauge theory on anisotropic lattices

The finite temperature transition of QCD can be seen as a change in the structure of the hadrons and as a symmetry breaking transition -- a change in the structure of the vacuum. These phenomena are observed differently and carry complementary information. We aim at a correlated analysis involving hadronic correlators and the vacuum structure including field and density correlations, both non-trivial questions.

QCD on the highly parallel computer AP1000

Abstract We have been running quenched QCD simulations on 32 4 and 32 3 × 48 lattices using a 512 processor AP1000, which is a highly parallel computer with up to 1024 processing elements. We have developed programs for update, blocking and hadron propagator calculations. The pseudo heatbath and the overrelaxation algorithms were used for the update with performance of 2.6 and 2.0 μsec/link, respectively.

Hadron spectroscopy on a 323 × 48 lattice

We report the first results of a hadron spectrum measurement by the QCD_TARO Collaboration with the massively parallel computer AP1000. The main memory of AP1000 is currently 8Gbytes (final goal : 16 Gbytes), which allows us to treat rather large lattices. We measure the quenched Wilson spectrum on a 323 × 48 lattice at β = 6.3. We obtain a good agreement with an empirical curve on the Edinburgh plot.

Systematic study of autocorrelation time in pure SU(3) lattice gauge theory

Abstract Results of our autocorrelation measurement performed on Fujitsu AP1000 are reported. We analyze (i) typical autocorrelation time, (ii) optimal mixing ratio between overrelaxation and pseudo-heatbath and (iii) critical behavior of autocorrelation time around cross-over region with high statistic in wide range of β for pure SU(3) lattice gauge theory on 8 4 , 16 4 and 32 4 lattices. For the mixing ratio K, small value (3–7) looks optimal in the confined region, and reduces the integrated autocorrelation time by a factor 2–4 compared to the pseudo-heatbath. On the other hand in the deconfined phase, correlation times are short, and overrelaxation does not seem to matter For a fixed value of K(=9 in this paper), the dynamical exponent of overrelaxation is close to 2. Autocorrelation measurement of the topological charge on 32 3 × 64 lattice at β = 6.0 is also briefly mentioned.

Monte Carlo renormalization group study at large β in confinement region

Abstract Monte Carlo renormalization group analysis on SU(3) lattice at large β is studied. On 32 4 lattice, coupling shift Δβ is 0.48 ± 0.02 and 0.53 ± 0.02 at β =6.55 and 6.80, where the lattice remains in confinement phase. Δβ is approaching its 2-loop asymptotic scaling value. However, deviation is still 20% and 13% at β =6.55 and 6.80, respectively. We also report high statistics data on 16 4 lattice at β =6.80, giving Δβ = .52 ± 0.03 in the deconfined regime.

Strange and charmed hadron spectroscopy on a 323 x 48 lattice at β = 6.3

The results of meson and baryon spectroscopy composed of charm and strange quarks are reported by the use of quenched Wilson fermions on a 323 x 48 lattice at β = 6.3. Ground state hadrons composed of two or three quarks with different hopping parameters, in a region κ = 0.13 to 0.15, are measured. It is found that their masses are well described by a quadratic polynomial in terms of multi-1/κ variables in this region. Adjusting vector meson mass ratios between (ss), (sc) and (cc), the hopping parameters of strange quark and charm quark are determined to be κs = 0.14999(22) and κc = 0.13548(82) without chiral extrapolation. Masses of not yet observed ssc, scc and ccc baryons in GeV are estimated to be 2.778 ± 0.0]6 (ssc), 3.858 ± 0.015 (scc) for (12)+ and 2.813 ± 0.167 (ssc), 3.869 ± 0.055 (scc) 4.880 ± 0.017 (ccc) for (3/2)+. As for the meson spin splitting structure, the quenched Wilson spectrum is more degenerate in comparison with real hadrons, as already pointed out by many authors.

Analyzing finite temperature mesonic correlators

We discuss problems related to the analysis of finite temperature general mesonic correlators and provide preliminary results on the pion wave function and dispersion law in quenched QCD at T ⋍ 0.9 Tc.

Does overrelaxed updating in lattice QCD improve critical slowing down

Abstract We study the autocorrelation time of blocked loops on 8 4 , 16 4 and 32 4 lattices in pure SU(3) lattice gauge theory over a wide range of β (= 6/ g 2 ) with high statistics. The critical exponent of integrated autocorrelation time by hybrid overrelaxation updating with fixed mixing ratio is found to be 1.74 ± 0.06. This suggests that the overrelaxation still suffer from critical slowing down toward the continuum limit.