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T. Kaneko

Publications and source records attributed to T. Kaneko.

At least 145 records · Page 8Linked to original sources
arXiv2003

Study of finite volume effects in the non-perturbative determination of $\csw$ with the SF method in full three-flavor lattice QCD

The non-perturbative $\csw$ determined by the Schrödinger functional (SF) method with the RG-improved gauge action in dynamical $N_f=3$ QCD shows a finite volume effect when the numerical simulations are carried out at a constant lattice size $L/a$. We remove the unwanted finite volume effect by keeping physical lattice extent $L$ at a constant. The details of the method and the result obtained for non-perturbative $\csw$ with a constant $L$ are reported.

hep-lat↗
arXiv2003

Continuum limit of proton decay matrix elements in quenched lattice QCD

We present a lattice QCD calculation of the parameters αand βwhich are necessary in the theoretical estimation of the proton lifetime in grand unified theories (GUTs) using chiral lagrangian approach. The simulation is carried out using the Wilson quark action at three gauge coupling constants in the quenched approximation. We obtain |α(2GeV)|=0.0091(08)(^{+10}_{-19})GeV^3 and |β(2GeV)|=0.0098(08)(^{+10}_{-20})GeV^3 in the continuum limit where the first error is statistical and the second one is due to scale setting.

hep-lat↗
arXiv2003

Light hadron spectroscopy with two flavors of $O(a)$-improved dynamical quarks

We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at β=5.2, where the lattice spacing is found to be a=0.0887(11)fm from ρmeson mass, on a 20^3\times 48 lattice. At each of five sea quark masses corresponding to m_{PS}/m_{V} \simeq 0.8-0.6, we generate 12000 trajectories using the symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 12^3 \times 48, 16^3 \times 48 lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find m_{ud}^{MS}(2GeV) =3.223(+0.046/-0.069)MeV and m_s^{MS}(2GeV)=84.5(+12.0/-1.7)MeV which are about 20% smaller than in quenched QCD.

hep-lat↗
arXiv2003

Full order_alpha electroweak and order alpha_s corrections to e^+e^- --> t t H

We present the full ${\cal O}(α)$ electroweak radiative corrections to associated Higgs top pair production in $e^+e^-$ collisions. We combine these results with a new calculation of the full one-loop QCD corrections. The computation is performed with the help of {\tt GRACE-loop}. We find that the ${\cal O}(α)$ correction can be larger than the ${\cal O}(α_s)$ corrections around the peak of the cross section especially for a light Higgs mass. At threshold these corrections are swamped by the QCD corrections which are enhanced by the gluon Coulomb contribution. We have also subtracted the complete QED corrections and expressed the genuine weak correction both in the $α$-scheme and the $G_μ$-scheme. This reveals that the genuine weak corrections are not negligible and should be taken into account for a precision measurement of this cross section and the extraction of the Yukawa $t \bar t H$ coupling.

hep-ph↗
arXiv2003

Non-Perturbative Determination of $c_{\rm SW}$ in Three-flavor Dynamical QCD

We present a fully non-perturbative determination of the $O(a)$ improvement coefficient $c_{\rm SW}$ in three-flavor dynamical QCD for the RG improved as well as the plaquette gauge actions, using the Schrödinger functional scheme. Results are compared with one-loop estimates at weak gauge coupling.

hep-lat↗
arXiv2003

An Exact Algorithm for Any-flavor Lattice QCD with Kogut-Susskind Fermion

We propose an exact simulation algorithm for lattice QCD with dynamical Kogut-Susskind fermion in which the N_f-flavor fermion operator is defined as the N_f/4-th root of the Kogut-Susskind (KS) fermion operator. The algorithm is an extension of the Polynomial Hybrid Monte Carlo (PHMC) algorithm to KS fermions. The fractional power of the KS fermion operator is approximated with a Hermitian Chebyshev polynomial, with which we can construct an algorithm for any number of flavors. The error which arises from the approximation is corrected by the Kennedy-Kuti noisy Metropolis test. Numerical simulations are performed for the two-flavor case for several lattice parameters in order to confirm the validity and the practical feasibility of the algorithm. In particular tests on a 16^4 lattice with a quark mass corresponding to m_{PS}/m_V ~ 0.68 are successfully accomplished. We conclude that our algorithm provides an attractive exact method for dynamical QCD simulations with KS fermions.

hep-lat↗
arXiv2003

Heavy quark expansion parameters from lattice NRQCD

We present a lattice QCD calculation of the heavy quark expansion parameters $μ_π^2$ and $μ_G^2$ for heavy-light mesons and heavy-light-light baryons. The calculation is carried out on a 20$^3\times$48 lattice at $β$ = 6.0 in the quenched approximation, using the lattice NRQCD action for heavy quarks. We obtain the parameters $μ_π^2$ and $μ_G^2$ in two different methods: a direct calculation of the matrix elements and an indirect calculation through the mass spectrum, and confirm that the both methods give consistent results. We also discuss an application to the lifetime ratios.

hep-lat↗
arXiv2003

Calculation of Non-Leptonic Kaon Decay Amplitudes from $K\toπ$ Matrix Elements in Quenched Domain-Wall QCD

We explore application of the domain wall fermion formalism of lattice QCD to calculate the $K\toππ$ decay amplitudes in terms of the $K\toπ$ and $K\to 0$ hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using domain-wall fermion action for quarks and an RG-improved gauge action for gluons on a $16^3\times 32\times 16$ and $24^3\times 32\times 16$ lattice at $β=2.6$ corresponding to the lattice spacing $1/a\approx 2$GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the $ΔI=1/2$ matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We confirm the chiral properties required of the $K\toπ$ matrix elements. Matching the lattice matrix elements to those in the continuum at $μ=1/a$ using the perturbative renormalization factor to one loop order, and running to the scale $μ=m_c=1.3$ GeV with the renormalization group for $N_f=3$ flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the $ΔI=3/2$ decay amplitude shows a good agreement with experiment in the chiral limit. The $ΔI=1/2$ amplitude, on the other hand, is about 50--60% of the experimental one even after chiral extrapolation. In view ofthe insufficient enhancement of the $ΔI=1/2$ contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of $ε'/ε$. We find that the $ΔI=3/2$ contribution is larger than the $ΔI=1/2$ contribution so that $ε'/ε$ is negative and has a magnitude of order $10^{-4}$. Possible reasons for these unsatisfactory results are discussed.

hep-lat↗
arXiv2002

Full one-loop electroweak radiative corrections to single Higgs production in e+ e-

We present the full ${\cal O}(α)$ electroweak radiative corrections to single Higgs production in \epemt. This takes into account the full one-loop corrections as well as the effects of hard photon radiation. We include both the fusion and Higgs-strahlung processes. The computation is performed with the help of {\tt GRACE-loop} where we have implemented a generalised non-linear gauge fixing condition. The latter includes 5 gauge parameters that can be used for checks on our results. Besides the UV, IR finiteness and gauge parameter independence checks it proves also powerful to test our implementation of the 5-point function. We find that for a 500GeV machine and a light Higgs of mass 150GeV, the total ${\cal O}(α)$ correction is small when the results are expressed in terms of $α_{\rm QED}$. The total correction decreases slightly for higher energies. For moderate centre of mass energies the total ${\cal O}(α)$ decreases as the Higgs mass increases, reaching -10% for $M_H=350$GeV and $\sqrt{s}=500$GeV. In order to quantify the genuine weak corrections we have subtracted the universal virtual and bremsstrahlung correction from the full ${\cal O}(α)$. We find, for $M_H=150$GeV, a weak correction slowly decreasing from -2% to -4% as the energy increases from $\sqrt{s}=300$GeV to $\sqrt{s}=1$TeV after expressing the tree-level results in terms of $G_μ$

hep-ph↗
arXiv2002

$B^0-\bar{B}^0$ mixing in quenched lattice QCD

We present our results of lattice calculations of $B$ parameters, which parameterize $ΔB$=2 transition amplitudes together with the leptonic decay constant. Calculations are made in the quenched approximation at $β$=5.7, 5.9, 6.0 and 6.1, using NRQCD action for heavy quark and the $O(a)$-improved Wilson action for light quark. The operators are perturbatively renormalized including the correction of $O(α_s/(aM)^m)$ ($m\ge$0). We examine the scaling behavior of $B$ parameters, and discuss the systematic uncertainties based on the results with several different truncations of higher order terms in 1/M and $α_s$ expansions. We find $B_{B_d}(m_b)=0.84(3)(5)$, $B_{B_s}/B_{B_d}=1.020(21)(^{+15}_{-16})(^{+5}_{-0})$ and $B_{S_s}(m_b)=0.85(1)(5)(^{+1}_{-0})$ in the quenched approximation. The errors represent statistical and systematic as well as the uncertainty in the determination of strange quark mass.

hep-lat↗
arXiv2002

Results for the Etaprime Mass from Two-Flavor Lattice QCD

We present results for the mass of the etaprime meson for two-flavor lattice QCD in the continuum limit, calculated on the CP-PACS computer, using an RG-improved gauge action and clover fermion action with tadpole-improved csw. Measurements are made at three couplings corresponding to a approx. 0.22, 0.16, 0.11 fm for four quark masses corresponding to mpi over mrho approx. 0.8, 0.75, 0.7, 0.6. Thw two-loop diagrams are evaluated using a noisy source method. Quark smearing for both one- and two- loop diagrams is successfully applied to obtain ground state signals in the etaprime channel. We obtain metaprime=0.960(87)+0.036-0.286GeV in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.

hep-lat↗
arXiv2002

Full O(alpha) corrections to e+e- --> nu nu-bar H by GRACE

We present the full O(alpha) corrections to single Higgs production in e+e- collision. The computation is performed with the help of GRACE-LOOP where a generalized non-linear gauge fixing condition is implemented. The numerical results are checked by testing their UV and IR finiteness as well as their independence on all five non-linear gauge parameters. We find that for a 500 GeV collider and a light Higgs boson of mass 150GeV, the total correction is small when the results are expressed in terms of alpha rather than G_mu. For a higher Higgs boson mass of 350GeV, the correction is of order -10%.

hep-ph↗
arXiv2002

I=2 Pion Scattering Phase Shift with Wilson Fermions

We present a lattice QCD calculation of the scattering phase shift for the I=2 $S$-wave two-pion system using the finite size method proposed by Lüscher. We work in the quenched approximation employing the standard plaquette action at $β=5.9$ for gluons and the Wilson fermion action for quarks. The phase shift is extracted from the energy eigenvalues of the two-pion system, which are obtained by a diagonalization of the pion 4-point function evaluated for a set of relative spatial momenta. In order to change momentum of the two-pion system, calculations are carried out on $24^3\times 60$, $32^3\times 60$, and $48^3\times 60$ lattices. The phase shift is successfully calculated over the momentum range $0 < p^2 < 0.3 {\rm GeV}^2$.

hep-lat↗
arXiv2002

I=2 Pion Scattering Length with the Wilson Fermion

The calculation of the I=2 pion scattering length in quenched lattice QCD is revisited. The calculation is carried out with the Wilson fermion action employing Lüscher's finite size scaling method at $β=5.9$, 6.1, and 6.3 corresponding to the range of lattice spacing $a\simeq 0.12 - 0.07$ fm. We obtain in the continuum limit $a_0m_π= -0.0410(69)$, which is consistent with the prediction of chiral perturbation theory $a_0m_π=-0.0444(10)$.

hep-lat↗
arXiv2002

Exploring QCD at small sea quark masses with improved Wilson-type quarks

We explore the region of small sea quark masses below $m_{PS}/m_V=0.5$ in two-flavor QCD using a mean-field improved clover quark action and an RG-improved gauge action at $a \simeq 0.2$ fm on $12^3 \times 24$ and $16^3 \times 24$ lattices. We find that instability of the standard BiCGStab algorithm at small quark masses can be mostly removed by the BiCGStab(DS-$L$) algorithm, which employs $L$-th minimal residual polynomials with a dynamical selection of $L$. We also find singular spikes of $ΔH$ in the HMC algorithm at moderate values of $Δτ$. Nature of the spike is studied. We also study finite-size effects and chiral properties of meson masses.

hep-lat↗
arXiv2002

I=2 Pion Scattering Phase Shift with Wilson Fermions

We present results of phase shift for I=2 $S$-wave $ππ$ system with the Wilson fermions in the quenched approximation. The finite size method proposed by Lüscher is employed, and calculations are carried out at $β=5.9$ ($a^{-1}=1.934(16)$ GeV from $m_ρ$) on $24^3 \times 60$, $32^3 \times 60$, and $48^3 \times 60$ lattices.

hep-lat↗
arXiv2002

Light hadron spectrum with two flavors of $O(a)$ improved dynamical quarks : final results from JLQCD

We present the final results of the JLQCD calculation of the light hadron spectrum and quark masses with two flavors of dynamical quarks using the plaquette gauge action and fully $O(a)$-improved Wilson quark action at $β=5.2$. We observe that sea quark effects lead to a closer agreement of the strange meson and baryon masses with experiment and a reduction of quark masses by about 25.

hep-lat↗