arXiv subjects

T. Onogi

Publications and source records attributed to T. Onogi.

At least 91 records · Page 5Linked to original sources

arXiv2001

Exploration of sea quark effects in two-flavor QCD with the O(a)-improved Wilson quark action

We explore sea quark effects in the light hadron mass spectrum in a simulation of two-flavor QCD using the nonperturbatively O(a)-improved Wilson fermion action. In order to identify finite-size effects, light meson masses are measured on 12^3x48, 16^3x48 and 20^3x48 lattices with a~0.1 fm. On the largest lattice, where the finite-size effect is negligible, we find a significant increase of the strange vector meson mass compared to the quenched approximation. We also investigate the quark mass dependence of pseudoscalar meson masses and decay constants and test the consistency with (partially quenched) chiral perturbation theory.

hep-lat↗

arXiv2001

O(a) improved Wilson quark action on anisotropic lattice

The $O(a)$ improved Wilson quark action on the anisotropic lattice is investigated. We carry out numerical simulations in the quenched approximation at three values of lattice spacing ($a_σ^{-1}=1$--2 GeV) with the anisotropy $ξ=a_σ/a_τ=4$, where $a_σ$ and $a_τ$ are the spatial and the temporal lattice spacings, respectively. Using the dispersion relation of mesons, the bare anisotropy $γ_F$ in the quark action is numerically tuned below the charm quark mass region with the statistical accuracy of 1 % level. The systematic uncertainties in the calibration are examined and found to be under control in the continuum limit. Then we compute the light hadron masses and find that they are consistent with the result of the UKQCD Collaboration on the isotropic lattice. The effect of the uncertainty in the calibration on the hadron spectrum for physical quark masses is also found to be under control.

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arXiv2001

Non-trivial phase structure of $N_f=3$ QCD with $O(a)$-improved Wilson fermion at zero temperature

JLQCD collaboration recently started the $N_f=3$ QCD simulations with the $O(a)$-improved Wilson fermion action employing an exact fermion algorithm developed for odd number of quark flavors. It is found that this theory has an unexpected non-trivial phase structure in the $(β,κ)$ plane even at zero temperature. A detailed study is made to understand the nature of the observed phase transitions and to find the way of avoiding untolerably large lattice artifacts associated with the phase transition.

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arXiv2001

An exact algorithm for three-flavor QCD with $O(a)$-improved Wilson fermions

We present an exact dynamical QCD simulation algorithm for the $O(a)$-improved Wilson fermion with odd number of flavors. Our algorithm is an extension of the non-Hermitian polynomials HMC algorithm proposed by Takaishi and de Forcrand previously. In our algorithm, the systematic errors caused by the polynomial approximation of the inverse of Dirac operator is removed by a noisy-Metropolis test. For one flavor quark it is achieved by taking the square root of the correction matrix explicitly. We test our algorithm for the case of $N_f=1+1$ on a moderately large lattice size ($16^3\times48$). The $N_f=2+1$ case is also investigated.

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arXiv2001

B meson B-parameters and the decay constant in two-flavor dynamical QCD

We present a two-flavor dynamical QCD calculation of the B meson B parameters and decay constant. We use NRQCD for heavy quark and the nonperturbatively O(a)-improved Wilson action for light quark at $β$=5.2 on a $20^3\times 48$ lattice. We confirm that the sea quark effect increases the heavy-light decay constant, while estimate of its magnitude depends significantly on the fitting form in the chiral extrapolation. For the B parameters, on the other hand, we do not find a significant sea quark effect. The chiral extrapolation with logarithmic term is examined for both quantities and compared with the prediction of ChPT.

hep-lat↗

arXiv2001

One-loop renormalization of heavy-light currents

We calculate the mass dependent renormalization factors of heavy-light bilinears at one-loop order of perturbation theory, when the heavy quark is treated with the Fermilab formalism. We present numerical results for the Wilson and Sheikholeslami-Wohlert actions, with and without tree-level rotation. We find that in both cases our results smoothly interpolate from the static limit to the massless limit. We also calculate the mass dependent Brodsky-Lepage-Mackenzie scale $q^*$, with and without tadpole-improvement.

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arXiv2001

Differential decay rate of $B \to πl ν$ semileptonic decay with lattice NRQCD

We present a lattice QCD calculation of $B\to πl ν$ semileptonic decay form factors in the small pion recoil momentum region. The calculation is performed on a quenched $16^3 \times 48$ lattice at $β=5.9$ with the NRQCD action including the full 1/M terms. The form factors $f_1(v\cdot k_π)$ and $f_2(v\cdot k_π)$ defined in the heavy quark effective theory for which the heavy quark scaling is manifest are adpoted, and we find that the 1/M correction to the scaling is small for the $B$ meson. The dependence of form factors on the light quark mass and on the recoil energy is found to be mild, and we use a global fit of the form factors at various quark masses and recoil energies to obtain model independent results for the physical differential decay rate. We find that the $B^*$ pole contribution dominates the form factor $f^+(q^2)$ for small pion recoil energy, and obtain the differential decay rate integrated over the kinematic region $q^2 >$ 18 GeV$^2$ to be $|V_{ub}|^2 \times (1.18 \pm 0.37 \pm 0.08 \pm 0.31)$ psec$^{-1}$, where the first error is statistical, the second is that from perturbative calculation, and the third is the systematic error from finite lattice spacing and the chiral extrapolation. We also discuss the systematic errors in the soft pion limit for $f^0(q^2_{max})$ in the present simulation.

hep-lat↗

arXiv2001

CP Violation in Seesaw Model

We study the structure of CP violating phases in the seesaw model. We find that the $3\times 6$ MNS matrix contains six independent phases, three of which are identified as a Dirac phase and two Majorana phases in the light neutrino sector while the remaining three arise from the mixing of the light neutrinos and heavy neutrinos. We show how to determine these phases from physical observables.

hep-ph↗

arXiv2000

Penguins diagrams in Delta I=1/2 rule and ε'/εwith σmodels

We study the correlation between $\epe$ and $ΔI=1/2$ rule in the framework of non-linear $σ$ model including scalar mesons. The matrix elements of QCD and Electroweak (EW) penguin operators are computed within factorization approximation. Using the matrix elements and changing the scalar meson mass, we find that there is correlation between $\epe$ and $ΔI=1/2$ amplitude. However, it is difficult to explain both $\epe$ and $ΔI=1/2$ amplitude simultaneously. In order to be compatible with $\epe$, typically, about half of $ΔI=1/2$ amplitude can be explained at most. Our result suggests there may be substantial non-factorizable contribution to CP conserving $K \to ππ$ amplitudes.

hep-ph↗

arXiv2000

Differential decay rate for $B \to πl ν$ semileptonic decays

We present our study on $B \to πl ν$ semileptonic decay form factors with NRQCD action for heavy quark from a quenched lattice QCD simulation at $β$=5.9 on a $16^3\times 48$ lattice. We obtain form factors defined in the context of heavy quark effective theory by Burdman et al. and find that their $1/m_B$ correction is small. The limit of physical heavy and light quark masses can be performed without introducing any model function, and we obtain a prediction for the differential decay rate $dΓ/dq^2$. We also discuss the soft pion limit of the form factors.

hep-lat↗

arXiv2000

B^0-\bar{B}^0 mixing with quenched lattice NRQCD

We present our recent results for the B-parameters, which parameterize the ΔB=2 transition amplitudes. Calculations are made in quenched QCD at β=5.7, 5.9, and 6.1, using NRQCD for heavy quark and the $O(a)$-improved action for light quark. The operators are perturbatively renormalized including corrections of O(α_s/am_Q). We examine scaling behavior of the B-parameters in detail, and discuss the systematic uncertainties using scatter of results with different analysis procedures adopted. As a result, we find B_{B_d}(m_b)=0.84(2)(8), B_{B_s}/B_{B_d}=1.017(10)(^{+4}_{-0}) and B_{S_s}(m_b)=0.87(1)(9)(^{+1}_{-0}) in the quenched approximation.

hep-lat↗

arXiv2000

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

We report on our study of light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Simulations are made with the plaquette gauge action and the non-perturbatively $O(a)$ improved Wilson quark action. We simulate 5 sea qaurk masses corresponding to $m_{PS}/m_{V} \simeq 0.8$--0.6 at $β=5.2$ on $12^3 \times 48$, $16^3 \times 48$ and $20^3 \times 48$ lattices. A comparison with previous calculations in quenched QCD indicates sea quark effects in meson and quark masses.

hep-lat↗

arXiv2000

Perturbative renormalization of the $ΔB=2$ four-quark operators in lattice NRQCD

We present a perturbative calculation of the renormalization constants for the $ΔB=2$ four-quark operators, which is needed to evaluate the bag parameters $B_B$ and $B_S$ in lattice QCD. The one-loop coefficients are calculated for the $O(1/M)$ NRQCD heavy quark action and the $O(a)$-improved Wilson action for light quark. Using these coefficients, which remove $O(α_s/aM)$ error, we reanalyze our previous calculation of the bag parameters.

hep-lat↗

arXiv2000

Renormalization of the ΔB=2 four-quark operators in lattice NRQCD

We calculate perturbative renormalization constants for the ΔB=2 four-quark operators in lattice NRQCD. Continuum operators \bar{b}γ_μ(1-γ_5)q~ \bar{b}γ_μ(1-γ_5)q and \bar{b}(1-γ_5)q~\bar{b}(1-γ_5)q, which are necessary in evaluating the mass and width differences in $B^0_{d(s)}-\bar{B}^0_{d(s)}$ systems, are matched at one-loop with corresponding lattice operators constructed from the NRQCD heavy quarks and the ${\cal O}(a)$-improved light quarks. Using these perturbative coefficients, we also reanalyse our previous simulation results for the matrix elements of the above operators. Our new results are free from the systematic error of ${\cal O}(α_s/(aM_b))$ in contrast to the previous ones with matching coefficients evaluated in the static limit.

hep-lat↗

arXiv2000

Width difference in the $B_s$-$\bar{B}_s$ system with lattice NRQCD

We compute the matrix element of the four-quark operator $\Op_S$ = $\bar{b}(1-γ_5) s \bar{b} (1-γ_5) s$ in the $B_s-\bar{B}_s$ mixing on the lattice using NRQCD, which gives a leading contribution in the calculation of the width difference $ΔΓ_s$ in the $1/m_b$ expansion. Using the next-to-leading formula of Beneke \textit{et al.}, we obtain $(ΔΓ/Γ)_s$ = 0.151(37)(36)(17), where the the first error reflects the uncertainty of $f_{B_s}$ = 245(30) MeV, the second error comes from our calculation of the matrix element of $\Op_S$, and the third represents unknown $1/m_b$ correction.

hep-ph↗

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

$B \to πl\barν$ 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.

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