arXiv subjects

S. Aoki

Publications and source records attributed to S. Aoki.

410 records · Page 23Linked to original sources

arXiv1995

On the phase structure of QCD with Wilson fermions

The phase structure of lattice QCD with Wilson fermions is discussed. Analytic and numerical evidences are given for the spontaneous breaking of parity and flavor symmetry, which naturally explains the existence of the massless pion at the critical hopping parameter $K_c$ without recourse to the chiral symmetry absent in the Wilson fermion formulation. New numerical evidences are also presented for the multiple structure of the critical lines in the weak coupling region. A connection between the phase structure and the finite temperature phase transition is briefly mentioned.

hep-lat↗

arXiv1995

Domain-wall fermions with $U(1)$ dynamical gauge fields

We have carried out a numerical simulation of a domain-wall model in $(2+1)$-dimensions, in the presence of a dynamical gauge field only in an extra dimension, corresponding to the weak coupling limit of a ( 2-dimensional ) physical gauge coupling. Using a quenched approximation we have investigated this model at $β_{s} ( = 1 / g^{2}_{s} ) =$ 0.5 ( ``symmetric'' phase), 1.0, and 5.0 (``broken'' phase), where $g_s$ is the gauge coupling constant of the extra dimension. We have found that there exists a critical value of a domain-wall mass $m_{0}^{c}$ which separates a region with a fermionic zero mode on the domain-wall from the one without it, in both symmetric and broken phases. This result suggests that the domain-wall method may work for the construction of lattice chiral gauge theories.

hep-lat↗

arXiv1995

Finite-Temperature Phase Structure of Lattice QCD with Wilson Quark Action

The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite-temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral tansition is examined. Analytical and numerical evidence are presented that the critical line forms a cusp at a finite gauge coupling, and the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed.

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

Kaplan-Narayanan-Neuberger lattice fermions pass a perturbative test

We test perturbatively a recent scheme for implementing chiral fermions on the lattice, proposed by Kaplan and modified by Narayanan and Neuberger, using as our testing ground the chiral Schwinger model. The scheme is found to reproduce the desired form of the effective action, whose real part is gauge invariant and whose imaginary part gives the correct anomaly in the continuum limit, once technical problems relating to the necessary infinite extent of the extra dimension are properly addressed. The indications from this study are that the Kaplan--Narayanan--Neuberger (KNN) scheme has a good chance at being a correct lattice regularization of chiral gauge theories.

hep-th↗

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↗

arXiv1993

Spontaneous Breaking of Flavor Symmetry and Parity in the Nambu-Jona-Lasinio Model with Wilson Fermions

We study the lattice \njl~model with two flavors of Wilson fermions in the large $N$ limit, where $N$ is the number of `colors'. For large values of the four-fermion coupling we find a phase in which both, flavor symmetry and parity, are spontaneously broken. In accordance with general expectations there are three massless pions on the phase boundary, but only two of them remain massless inside the broken phase. This is analogous to earlier results obtained in lattice QCD, indicating that this behavior is a very general feature of the Wilson term.

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↗

arXiv1993

Perturbative analysis for Kaplan's lattice chiral fermions

Perturbation theory for lattice fermions with domain wall mass terms is developed and is applied to investigate the chiral Schwinger model formulated on the lattice by Kaplan's method. We calculate the effective action for gauge fields to one loop, and find that it contains a longitudinal component even for anomaly-free cases. From the effective action we obtain gauge anomalies and Chern-Simons current without ambiguity. We also show that the current corresponding to the fermion number has a non-zero divergence and it flows off the wall into the extra dimension. Similar results are obtained for a proposal by Shamir, who used a constant mass term with free boundaries instead of domain walls.

hep-lat↗

arXiv1993

Anomaly through Gauge Invariant Regularization with Infinite Number of Pauli-Villars Fields

Abelian anomaly is examined by means of the recently proposed gauge invariant regularization for SO(10) chiral gauge theory and its generalization for a theory of arbitrary gauge group with anomaly-free chiral fermion contents. For both cases it is shown that the anomaly with correct normalization can be obtained in a gauge invariant form without any counterterms.

hep-th↗

arXiv1993

Charged fermion states in the quenched U(1) chiral Wilson-Yukawa model

Property of charged fermion states is investigated in the quenched U(1) chiral Wilson-Yukawa model. Fitting the charged fermion propagator with a single hyperbolic cosine does not yield reliable results. On the other hand the behavior of the propagator including large lattice size dependence is well described by the large Wilson-Yukawa coupling expansion, providing strong evidence that no charged fermion state exists as an asymptotic particle in this model.

hep-lat↗

arXiv1992

The Spectrum of the Kazakov Migdal-Model

Gross has found an exact expression for the density of eigenvalues in the simplest version of the Kazakov-Migdal model of induced QCD. In this paper we compute the spectrum of small fluctuations around Gross's semi-circular solution. By solving Migdal's wave equation we find a string-like spectrum which, in four dimensions, corresponds to the infinite tower of mesons in strong coupling lattice QCD with adjoint matter. In one dimension our formula reproduces correctly the well known spectrum of the hermitean matrix model with a harmonic oscillator potential. We comment on the relevance of our results to the possibility of the model describing extended objects in more than one dimension.

hep-lat↗

arXiv1992

Fermion spectrum in the quenched U(1) chiral Wilson-Yukawa model

Nature of charged fermion state is investigated in the quenched U(1) chiral Wilson-Yukawa model. Fitting the charged fermion propagator with a single hyperbolic cosine does not yield reliable result. On the other hand the behaviour of the propagator including large lattice size dependence is well described by the large Wilson-Yukawa coupling expansion, providing strong evidence that no charged state exists as an asymptotic particle in this model.

hep-lat↗