arXiv subjects

A. Ukawa

Publications and source records attributed to A. Ukawa.

188 records · Page 11Linked to original sources

arXiv1994

Scalar and axial vector matrix elements of proton in quenched QCD: Calculation of both connected and disconnected contributions

$π$-$N$ $σ$ term and proton axial vector matrix elements are calculated including disconnected contributions with a variant wall source method using the Wilson quark action at $β=5.7$ in quenched QCD. For the $σ$ term, we find $σ_{disc}/σ_{conn}=2.35(46)$ and $σ=44(6)$MeV--60(9)MeV. The fraction of proton spin carried by quarks is $ΔΣ=Δ{u}+Δ{d}+Δ{s}=+0.638(54)-0.347(46)-0.109(30)= +0.18(10)$.

hep-lat↗

arXiv1994

Charmonium spectroscopy with heavy Kogut-Susskind quarks

Charmonium spectroscopy with Kogut-Susskind valence quarks are carried out for quenched QCD at $β=6.0$ and for two-flavor full QCD at $β=5.7$. Results for 1P--1S mass splitting and estimates of $α^{(5)}_{\overline{MS}}(m_Z)$ are reported. Problems associated with flavor breaking effects and finite size effects of $1P$ states are discussed.

hep-lat↗

arXiv1994

Pion-Nucleon Sigma Term in Lattice QCD

We calculate both connected and disconnected contribution to the $π$-$N$ $σ$-term in quenched lattice QCD with Wilson quark action on a $12^3\times 20$ lattice at $β=5.7$. The latter is evaluated with the aid of the variant wall source method, which was previously applied successfully for extraction of $π$-$π$ scattering lengths and $η^\prime$ meson mass. We found that the disconnected contribution is about twice larger than the connected one. The value for the full $π$-$N$ $σ$ term $σ=40-60$ MeV is consistent with the experimental estimates. The nucleon matrix element of the strange quark density $\bar s s$ is fairly large in our result.

hep-lat↗

arXiv1994

Manifestation of Sea Quark Effects in the Strong Coupling Constant in Lattice QCD

We demonstrate that sea quark effects of a magnitude expected from renormalization group considerations are clearly visible in the strong coupling constant measured in current full QCD simulations. Building on this result an estimate of $α_{\overline{MS}}^{(5)}(M_Z)$ is made employing the charmonium $1S-1P$ mass splitting calculated on full QCD configurations generated with two flavors of dynamical Kogut-Susskind quarks to fix the scale.

hep-lat↗

arXiv1994

An Exploratory Study of Nucleon-Nucleon Scattering Lengths in Lattice QCD

An exploratory study is made of the nucleon-nucleon $s$-wave scattering lengths in quenched lattice QCD with the Wilson quark action. The $π$-$N$ and $π$-$π$ scattering lengths are also calculated for comparison. The calculations are made with heavy quarks corresponding to $m_π/m_ρ\approx 0.73-0.95$. The results show that the $N$-$N$ system has an attractive force in both spin-singlet and triplet channels, with their scattering lengths significantly larger than those for the $π$-$N$ and $π$-$π$ cases, a trend which is qualitatively consistent with the experiment. Problems toward a more realistic calculation for light quarks are discussed.

hep-lat↗

arXiv1993

Lattice QCD Calculation of Hadron Scattering Lengths

Method of calculating hadron multi-point functions and disconnected quark loop contributions which are not readily accessible through conventional techniques is proposed. Results are reported for pion-pion, pion-nucleon and nucleon-nucleon scattering lengths and the flavor singlet-non singlet meson mass splitting estimated in quenched QCD.

hep-lat↗

arXiv1993

Finite-Size Effect of Hadron Masses with Kogut-Susskind Quarks

We present numerical results and their analyses of finite-size effects of hadron masses for both quenched and full QCD calculations. We show that they are much larger for full QCD due to dynamical sea quarks and the associated breaking of $Z(3)$ symmetry. We also argue that finite-size effects are non-negligible even for the largest lattice size simulation currently being made for a very small quark mass. (talk at lattice93)

hep-lat↗

arXiv1993

Sea Quark Effects on the Strong Coupling Constant

We present results showing that the strong coupling constant measured in two-flavor full QCD with dynamical Kogut-Susskind quarks at $β=5.7$ exhibit a 15\% increase due to sea quarks over that for quenched QCD at the scale $μ\approx 7$GeV . (talk at lattice93)

hep-lat↗