arXiv subjects

S. Aoki

Publications and source records attributed to S. Aoki.

At least 343 records · Page 19Linked to original sources

arXiv2000

Dynamical Quark Effects on Light Quark Masses

We present results for light quark masses from a systematic lattice QCD study with two degenerate flavors of dynamical quarks. Simulations are made with a renormalization-group improved gauge action and a mean-field improved clover quark action for sea quark masses corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 and the lattice spacing $a=0.22$--0.11 fm. In the continuum limit we find $m_{ud}^{\bar{MS}}(2 {\rm GeV})=3.44^{+0.14}_{-0.22}$ MeV using the $π$ and $ρ$ meson masses as physical input, and $m_s^{\bar{MS}}(2 {\rm GeV})=88^{+4}_{-6}$ MeV or $90^{+5}_{-11}$ MeV with the $K$ or $ϕ$ meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about 25%.

hep-lat↗

arXiv2000

Chiral properties of domain-wall quarks in quenched QCD

We investigate the chiral properties of quenched domain-wall QCD (DWQCD) at the lattice spacings $a^{-1} \simeq 1$ and 2 GeV for both plaquette and renormalization-group (RG) improved gauge actions. In the case of the plaquette action we find that the quark mass defined through the axial Ward-Takahashi identity remains non-vanishing in the DWQCD chiral limit that the bare quark mass $m_f\to 0$ and the length of the fifth dimension $N_s\to\infty$, indicating that chiral symmetry is not realized with quenched DWQCD up to $a^{-1} \simeq 2$ GeV. The behavior is much improved for the RG-improved gauge action: while a non-vanishing quark mass remains in the chiral limit at $a^{-1}\simeq 1$ GeV, the result at $a^{-1}\simeq 2$ GeV is consistent with an exponentially vanishing quark mass in the DWQCD chiral limit, indicating the realization of exact chiral symmetry. An interpretation and implications are briefly discussed.

hep-lat↗

arXiv2000

Perturbative Renormalization Factors of Baryon Number Violating Operators for Improved Quark and Gauge Actions in Lattice QCD

We calculate one-loop renormalization factors of three-quark operators, which appear in the low energy effective Lagrangian of the nucleon decay, for $O(a)$-improved quark action and gauge action including six-link loops. This calculation is required to predict the hadronic nucleon decay matrix elements in the continuum regularization scheme using lattice QCD. We present detailed numerical results of the one-loop coefficients for general values of the clover coefficients employing the several improved gauge actions in the Symanzik approach and in the Wilson's renormalization group approach. The magnitudes of the one-loop coefficients for the improved gauge actions show sizable reduction compared to those for the plaquette action.

hep-lat↗

arXiv1999

Pion decay constant for the Kogut-Susskind quark action in quenched lattice QCD

We present a study for the pion decay constant $f_π$ in the quenched approximation to lattice QCD with the Kogut-Susskind (KS) quark action, with the emphasis given to the renormalization problems. Numerical simulations are carried out at the couplings $β= 6.0$ and 6.2 on $32^3\times 64$ and $48^3\times 64$ lattices, respectively. The pion decay constant is evaluated for all KS flavors via gauge invariant and non-invariant axial vector currents with the renormalization constants calculated by both non-perturbative method and perturbation theory. We obtain $f_π= 89(6)$ MeV in the continuum limit as the best value using the partially conserved axial vector current, which requires no renormalization. From a study for the other KS flavors we find that the results obtained with the non-perturbative renormalization constants are well convergent among the KS flavors in the continuum limit, confirming restoration of $\rm SU(4)_A$ flavor symmetry, while perturbative renormalization still leaves an apparent flavor breaking effect even in the continuum limit.

hep-lat↗

arXiv1999

Heavy-light spectrum and decay constant from NRQCD with two flavors of dynamical quarks

We report on a study of B mesons on N_f = 2 full QCD configurations using an RG-improved gauge action, NRQCD heavy quark action and tadpole-improved clover light quark action. Results on the heavy-light spectrum and the decay constants from 16^3x32 lattices at a^{-1} ~ 1.5 GeV are presented, and compared with quenched results obtained with the same action combination at matching lattice spacings.

hep-lat↗

arXiv1999

$B \to πl\barν$ Form Factors with NRQCD Heavy Quark and Clover Light Quark Actions

We report results on semileptonic $B\toπl\barν$ decay form factors near $q^2_{\rm max}$ using NRQCD heavy quark and clover light quark actions and currents improved through $O(αa)$. An inconsistency with the soft pion relation $f^0(q^2_{\rm max})= f_B/f_π$ found in a previous work is confirmed, and a possible solution with nonperturbative renormalization is discussed. We find that $f^+(q^2)$ is well described by the $B^*$ pole near $q^2_{\rm max}$, and its $1/M_B$ scaling is also consistent with the prediction of the pole dominance model.

hep-lat↗

arXiv1999

Nucleon Decay Matrix Elements from Lattice QCD

We present a model-independent calculation of hadron matrix elements for all dimension-six operators associated with baryon number violating processes using lattice QCD. The calculation is performed with the Wilson quark action in the quenched approximation at $β=6/g^2=6.0$ on a $28^2\times 48\times 80$ lattice. Our results cover all the matrix elements required to estimate the partial lifetimes of (proton,neutron)$\to$($π,K,η$) +(${\bar ν},e^+,μ^+$) decay modes. We point out the necessity of disentangling two form factors that contribute to the matrix element; previous calculations did not make the separation, which led to an underestimate of the physical matrix elements. With a correct separation, we find that the matrix elements have values 3-5 times larger than the smallest estimates employed in phenomenological analyses of the nucleon decays, which could give strong constraints on several GUT models. We also find that the values of the matrix elements are comparable with the tree-level predictions of chiral lagrangian.

hep-lat↗

arXiv1999

I=2 Pion Scattering Length with Wilson Fermions

We present results for I=2 pion scattering length with the Wilson fermions in the quenched approximation. The finite size method presented by Lüscher is employed, and calculations are carried out at $β=5.9$, 6.1, and 6.3. In the continuum limit, we obtain a result in reasonable agreement with the experimental value.

hep-lat↗

arXiv1999

Pion decay constant in quenched QCD with Kogut-Susskind quarks

We present a non-perturbative calculation for the pion decay constant with quenched Kogut-Susskind quarks. Numerical simulations are carried out at $β= 6.0$ and 6.2 with various operators extending over all flavors. The renormalization correction is applied for each flavor by computing non-perturbative renormalization constants, and it is compared with a perturbative calculation. We also study the behavior of $f_π$ in the continuum limits for both non-perturbative and perturbative calculations. The results in the continuum limit is also discussed.

hep-lat↗

arXiv1999

Nucleon decay matrix elements with the Wilson quark action: an update

We present preliminary results of a new lattice computation of hadronic matrix elements of baryon number violating operators which appear in the low-energy effective Lagrangian of (SUSY-)Grand Unified Theories. The contribution of irrelevant form factor which has caused an underestimate of the matrix elements in previous studies is subtracted in this calculation. Our results are 2$\sim$4 times larger than the most conservative values often employed in phenomenological analyses of nucleon decay with specific GUT models.

hep-lat↗

arXiv1999

Lattice QCD with Domain-Wall Fermions

We study the quenched lattice QCD using domain-wall fermions at $β=6.0$. Behaviors of both pion mass and the explicit breaking term in the axial Ward-Takahashi identity support the existence of the chiral zero modes. We observe a good agreement between the pion decay constants $f_π$ from both the conserved axial current and the local current perturbatively renormalized at 1-loop. Finally the possible existence of the parity broken phase is also examined in this model.

hep-lat↗

arXiv1999

Heavy Quarkonia from Anisotropic and Isotropic Lattices

We report on recent results for the spectrum of heavy quarkonia. Using coarse and anisotropic lattices we achieved an unprecedented control over statistical and systematic errors for higher excited states such as exotic hybrid states. In a parallel study on isotropic lattices we also investigate the effect of two dynamical flavours on the spin structure of charmonium and bottomonium for several symmetric lattices.

hep-lat↗

arXiv1999

Heavy-light decay constants from relativistic Nf=2,0 QCD

We present results on an analysis of the decay constants fB and fBs with two flavours of sea quark. The calculation has been carried out on 3 different bare gauge couplings and 4 sea quark masses at each gauge coupling, with m_pi/m_rho ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform calculations with heavy quarks whose mass is in the range of the b-quark. A comparison with a quenched calculation using the same action is made to elucidate the effects due to the sea quarks.

hep-ph↗

arXiv1999

Equation of state for pure SU(3) gauge theory with renormalization group improved action

A lattice study of the equation of state for pure SU(3) gauge theory using a renormalization-group (RG) improved action is presented. The energy density and pressure are calculated on a $16^3\times 4$ and a $32^3\times 8$ lattice employing the integral method. Extrapolating the results to the continuum limit, we find the energy density and pressure to be in good agreement with those obtained with the standard plaquette action within the error of 3-4%.

hep-lat↗

arXiv1999

Equation of state for pure SU(3) gauge theory with RG improved action

We present results for the equation of state for pure SU(3) gauge theory obtained with a renormalization-group (RG) improved action. The energy density and pressure are calculated on a $16^3\times 4$ and a $32^3\times 8$ lattice employing the integral method. Extrapolating the results to the continuum limit, we find the energy density and pressure to be in good agreement with those obtained with the standard plaquette action within the error of 3-4%.

hep-lat↗

arXiv1999

Equation of state in finite-temperature QCD with improved Wilson quarks

We study finite-temperature phase transition and equation of state for two-flavor QCD at $N_t=4$ using an RG-improved gauge action and a meanfield-improved clover quark action. The pressure is computed using the integral method. The O(4) scaling of chiral order parameter is also examined.

hep-lat↗

arXiv1999

Light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks

We present updated results of the CP-PACS calculation of the light hadron spectrum in $N_{\rm f}=2$ full QCD. Simulations are made with an RG-improved gauge action and a tadpole-improved clover quark action for sea quark masses corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 and the lattice spacing $a=0.22$--0.09 fm. A comparison of the full QCD spectrum with new quenched results, obtained with the same improved action, shows clearly the existence of sea quark effects in vector meson masses. Results for light quark masses in $N_{\rm f}=2$ QCD are also presented.

hep-lat↗

arXiv1999

Heavy-light decay constants from clover heavy quark action in QCD with two flavors of dynamical quarks

We present results on an analysis of the decay constants f_B and f_Bs with two flavours of sea quark. The calculation has been carried out on 3 different bare gauge couplings and 4 sea quark masses at each gauge coupling, with m_pi/m_rho ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform calculations with heavy quarks whose mass is in the range of the b-quark. A detailed comparison with a quenched calculation using the same action is made to elucidate the effects due to the sea quarks.

hep-lat↗