arXiv subjects

S. Aoki

Publications and source records attributed to S. Aoki.

At least 379 records · Page 21Linked to original sources

arXiv1997

The domain-wall model in an asymptotic-free dynamics

We investigate a possibility that the rough gauge problem, which have appeared to be a main reason for failures of lattice chiral gauge theories, is cured by an asymptotic-free dynamics. Taking the domain-wall model in 2(+1) dimensions with SU(2) gauge group, we carry out the quenched simulation of gauge fields in the extra dimension. By studying fermion spectra in several volumes, we show that the chiral zero modes exist on the wall without having the spontaneous symmetry breaking thanks to the asymptotic-free dynamics. This result suggests that the rough gauge problem is solved in some class of lattice chiral fermions as well as in 4 dimensions if an asymptotic-free dynamics is incorporated.

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arXiv1997

B meson decay constant from quenched Lattice QCD

A lattice QCD calculation of the B meson decay constant is presented. In order to investigate the scaling violation associated with the heavy quark, parallel simulations are carried out employing both Wilson and the O(a)-improved clover actions for the heavy quark. The discretization errors due to the large $b$ quark mass are estimated in a systematic way with the aid of the non-relativistic interpretation approach of El-Khadra, Kronfeld and Mackenzie. As our best value from the quenched simulations at $β$=5.9, 6.1 and 6.3 we obtain $f_B$=163$\pm$16 MeV and $f_{B_s}$=175$\pm$18 MeV in the continuum limit where the error includes both statistical and systematic uncertainties.

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arXiv1997

B meson decay constant with the Wilson and Clover heavy quark actions

We present results of our quenched study of the B meson decay constant obtained with a parallel set of simulations with the Wilson and Clover actions at β=5.9, 6.1 and 6.3. Systematic errors associated with the large b-quark mass are analyzed within the Fermilab non-relativistic formalism. As our best estimate in the continuum limit we obtain $f_B=163 \pm 16 MeV$ and $f_{B_s}=175 \pm 18 MeV$ with the Clover action.

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arXiv1997

Heavy quark mass dependence of semileptonic form factors for B decays

We present our study of the dependence of the heavy-to-light semileptonic B decay form factors on the heavy-light meson mass $M_{PS}$. Simulations are made over a range of the heavy quark mass covering both the charm and bottom quarks using the $O(a)$-improved clover action at $β=5.9$ on a $16^3\times 40$ and $24^3\times 64$ lattice. We find that a weak dependence of form factors on $M_{PS}$ observed in previous studies in the region of charm quark persists up to the region of$b$ quark. The soft pion relation $f^0(q^2_{max})=f_B/f_π$ is examined and found to be largely violated.

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arXiv1997

The Kaon B-parameter with the Wilson Quark Action using Chiral Ward Identities

We present a detailed description of the method and results of our calculation of the kaon B parameter using the Wilson quark action in quenched QCD at $β=5.9-6.5$. The mixing problem of the $Δs=2$ four-quark operators is solved non-perturbatively with full use of chiral Ward identities. We find $B_K(NDR, 2 GeV)=0.562(64)$ in the continuum limit, which agrees with the value obtained with the Kogut-Susskind quark action.

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arXiv1997

The Light Quark Masses with the Wilson Quark Action using Chiral Ward Identities

We present results for the light quark masses for the Wilson quark action obtained with the PCAC relation for the one-link extended axial vector current in quenched QCD at $β=5.9-6.5$. This method leads to a remarkable improvement of scaling behavior of the light quark masses compared to the conventional method. We obtain ${\bar m}_l=3.87(37)$MeV for the averaged up and down quark mass and ${\bar m}_s=97(9)$MeV for the strange quark mass in the ${\barMS}$ scheme at $μ=2$GeV.

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arXiv1997

$K^{+}\toπ^{+}π^{0}$ Decay Amplitude in Quenched Lattice QCD

A new study is reported of a lattice QCD calculation of the $K^+\toπ^+ π^0 $ decay amplitude with the Wilson quark action in the quenched approximation at $β=6.1$. The amplitude is extracted from the $K\toππ$ Green function, and a conversion to the continuum value is made employing a recent one-loop calculation of chiral perturbation theory. The result is consistent with the experimental value if extrapolated to the chiral limit.

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arXiv1997

Perturbative renormalization parameters for heavy quarks

We study the heavy quark mass dependence of the perturbative renormalization factors for the heavy-light currents involving Wilson, Clover, and NRQCD heavy quarks. We find that the one-loop Z-factor for the axial-vector current depends significantly on the heavy quark mass commonly for all actions we study, while that for the vector current has smaller dependence.

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arXiv1997

One loop calculation in lattice QCD with domain-wall quarks

One loop corrections to the domain-wall quark propagator are calculated in massless QCD. It is shown that no additative counter term to the current quark mass is generated in this theory, and the wave function renormalization factor of the massless quark is explicitly evaluated. We also show that an analysis with a simple mean-field approximation can explain properties of the massless quark in numerical simulations of QCD with domain-wall quarks.

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arXiv1997

Kaon B parameter from quenched Lattice QCD

We present results of a large-scale simulation for the Kaon B parameter $B_K$ in quenched lattice QCD with the Kogut-Susskind quark action. Calculating $B_K$ at 1% statistical accuracy for seven values of lattice spacing in the range $a\approx 0.24-0.04$ fm on lattices up to $56^3\times 96$, we verify a quadratic $a$ dependence of $B_K$ theoretically predicted. Strong indications are found that, with our level of accuracy, $α_{\bar{MS}}(1/a)^2$ terms arising from our one-loop matching procedure have to be included in the continuum extrapolation. We present $B_K$(NDR, 2 GeV)=0.628(42) as our final value, as obtained by a fit including the $α_{\bar{MS}}(1/a)^2$ term.

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arXiv1997

Hadron spectroscopy and static quark potential in full QCD: A comparison of improved actions on the CP-PACS

We present first results from a full QCD calculation on the CP-PACS, comparing various actions at $a^{-1} \sim 1 GeV$ and $m_π/m_ρ\approx 0.7$--0.9. We use the plaquette and a renormalization group improved action for the gluons, and the Wilson and the SW-Clover action for quarks. We find that significant improvements in the hadron spectrum results from improving the quarks, while the gluon improvement is required for a rotationally invariant static potential. An ongoing effort towards exploring the chiral limit in full QCD is described.

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arXiv1997

CP-PACS results for quenched QCD spectrum with the Wilson action

We present progress report of a CP-PACS calculation of quenched QCD spectrum with the Wilson quark action. Light hadron masses and meson decay constants are obtained at $β=$5.9, 6.1, and 6.25 on lattices with a physical extent of 3 fm, and for the range of quark mass corresponding to $m_π/m_ρ\approx 0.75$ $-$ 0.4. Nucleon mass at each $β$ appears to be a convex function of quark mass, and consequently the value at the physical quark mass is much smaller than previously thought. Hadron masses extrapolated to the continuum limit exhibits a significant deviation from experimental values: with $K$ meson mass to fix strange quark mass, strange meson and baryon masses are systematically lower. Light quark masses determined from the axial Ward identity are shown to agree with those from perturbation theory in the continuum limit. Decay constants of mesons are also discussed.

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arXiv1997

Results for Quenched $B_K$ from JLQCD

A report is presented on our continued effort to elucidate the continuum limit of $B_K$ using the quenched Kogut-Susskind quark action. By adding to our previous simulations one more point at $β= 6.65$ employing a $56^3\times 96$ lattice, we now confirm the expected $O(a^2)$ behavior of $B_K$ with the Kogut-Susskind action. A simple continuum extrapolation quadratic in $a$ leads to $B_K$(NDR, 2 GeV) = 0.598(5). As our final value of $B_K$ in the continuum we present $B_K$(NDR, 2 GeV)=0.628(42), as obtained by a fit including an $α_{\bar{MS}}(1/a)^2$ term arising from the lattice-continuum matching with the one-loop renormalization.

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arXiv1997

Two-Flavor Chiral Phase Transition in Lattice QCD with the Kogut-Susskind Quark Action

A summary is presented of a scaling study of the finite-temperature chiral phase transition of two-flavor QCD with the Kogut-Susskind quark action based on simulations on $L^3\times4$ ($L$=8, 12 and 16) lattices at the quark mass of $m_q=0.075, 0.0375, 0.02$ and 0.01. We find a phase transition to be absent for $m_q\geq 0.02$, and also quite likely at $m_q=0.01$. The quark mass dependence of susceptibilities is consistent with a second-order transition at $m_q=0$. The exponents, however, deviate from the O(2) and O(4) values theoretically expected.

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arXiv1997

Scaling Study of the Two-Flavor Chiral Phase Transition with the Kogut-Susskind Quark Action in Lattice QCD

We report on a study of two-flavor finite-temperature chiral phase transition employing the Kogut-Susskind quark action and the plaquette gluon action in lattice QCD for a lattice with $N_t=4$ temporal size. Hybrid R simulations of $10^4$ trajectories are made at quark masses of $m_q=0.075, 0.0375, 0.02, 0.01$ in lattice units for the spatial sizes $8^3, 12^3$ and $16^3$. The spatial size dependence of various susceptibilities confirm the previous conclusion of the absence of a phase transition down to $m_q=0.02$. At $m_q=0.01$ an increase of susceptibilities is observed up to the largest volume $16^3$ explored in the present work. We argue, however, that this increase is likely to be due to an artifact of too small a lattice size and it cannot be taken to be the evidence for a first-order transition. Analysis of critical exponents estimated from the quark mass dependence of susceptibilities shows that they satisfy hyperscaling consistent with a second-order transition located at $m_q=0$. The exponents obtained from larger lattice, however, deviate significantly from both those of O(2), which is the exact symmetry group of the Kogut-Susskind action at finite lattice spacing, and those of O(4) expected from an effective sigma model analysis in the continuum limit.

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arXiv1997

Finite-temperature chiral transitions in QCD with the Wilson quark action

We investigate the finite-temperature phase structure and the scaling of the chiral condensate in lattice QCD with two degenerate light quarks, using a renormalization group improved gauge action and the Wilson quark action. We obtain a phase diagram which is consistent with that from the parity-flavor breaking scenario. The scaling relation for the chiral condensate assuming the critical exponents and the scaling function of the three dimensional O(4) model is remarkably satisfied for a wide range of parameters. This indicates that the chiral transition in two flavor QCD is of second order in the continuum limit.

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arXiv1997

CP-PACS Result for the Quenched Light Hadron Spectrum

The quenched hadron spectrum in the continuum obtained with the Wilson quark action in recent simulations on the CP-PACS is presented. Results for the light quark masses and the QCD scale parameter are reported.

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arXiv1997

One loop calculation of QCD with domain-wall quarks

We calculate one loop corrections to the domain-wall quark propagator in QCD. We show how the wave function is renormalized in this theory. Especially we are interested in the behavior of the massless fermion mode, which exists near the domain wall at the tree level. We show that this massless mode is stable against the quantum correction.

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