arXiv subjects

Tetsuya Onogi

Publications and source records attributed to Tetsuya Onogi.

At least 73 records · Page 4Linked to original sources

arXiv2009

Search for the IR fixed point in the twisted Polyakov loop scheme

We present a non-perturbative study of the running coupling constant in the Twisted Polyakov Loop (TPL) scheme. We investigate how the systematic and statistical errors can be controlled {\it via} a feasibility study in SU(3) pure Yang-Mills theory. We show that our method reproduces the perturbative determination of the running coupling in the UV. In addition, our numerical result agrees with the theoretical prediction of this coupling constant in the IR. We also present our preliminary results for $N_f=12$ QCD, where an IR fixed point may be present.

hep-lat↗

arXiv2009

Progress in lattice QCD

I review the recent progress in lattice QCD, which will be useful in heavy quark physics in the near future. Reviewing the theoretical developments in lattice QCD first, I focus our recent unquenched QCD with dynamical overlap fermion as implemented by JLQCD collaboration. I also introduce some of our recent studies on the B^*Bπcoupling and on the determination of |V_{ub}| through the dispersive bound.

hep-ph↗

arXiv2008

A New Method of Calculating the Running Coupling Constant

We propose a new method to compute the running coupling constant of gauge theories on the lattice. We first give the definition of the running coupling in the new scheme using the Wilson loops in a finite volume, and explain how the running of the coupling constant is extracted from the measurement of the volume dependence. The perturbative calculation of the renormalization constant to define the scheme is also given at the leading order. As a benchmark test of the new scheme we apply the method the case of the quenched QCD. We show the preliminary result from our numerical simulations which are carried out with plaquette gauge action for various lattice sizes and bare lattice couplings. With techniques to improve the statistical accuracy, we show that we can determine the non-perturbative running of the coupling constant in a wide range of the energy scale with relatively small number of gauge configurations in our scheme. We compare our lattice data of the running coupling constant with perturbative renormalization group evolution at one- and two-loop order, and confirm the consistency between them at high energy.

hep-lat↗

arXiv2008

Determination of B*B pi coupling in unquenched QCD

The $B^* Bπ$ coupling is a fundamental parameter of chiral effective Lagrangian with heavy-light mesons and can constrain the chiral behavior of $f_B$, $B_B$ and the $B\to πl ν$ form factor in the soft pion limit. We compute the $B^* B π$ coupling with the static heavy quark and the $O(a)$-improved Wilson light quark. Simulations are carried out with $n_f=2$ unquenched $12^3\times 24$ lattices at $β=1.80$ and $16^3\times 32$ lattices at $β=1.95$ generated by CP-PACS collaboration. To improve the statistical accuracy, we employ the all-to-all propagator technique and the static quark action with smeared temporal link variables following the quenched study by Negishi {\it et al.}. These methods successfully work also on unquenched lattices, and determine the $B^*Bπ$ coupling with 1--2% statistical accuracy on each lattice spacing.

hep-lat↗

arXiv2007

High precision study of B*B pi coupling in unquenched QCD

The B* B pi coupling is a fundamental parameter of chiral effective Lagrangian with heavy-light mesons and can constrain the B->pi l nu form factor in the soft pion limit which will be useful for precise determination of |Vub|. We compute the B* B pi coupling with the static heavy quark and the O(a)-improved Wilson light quark. Simulations are carried out with n_f=2 unquenched 12^3x24 lattices at beta=1.80 generated by CP-PACS collaboration. Following the quenched study by Negishi et al., we employ the all-to-all propagator with 200 low eigenmodes as well as HYP smeared link to improve the statistical accuracy.

hep-lat↗

arXiv2007

Theta vacuum physics from QCD at fixed topology

We propose a method to obtain physical quantities in the theta vacuum from those at fixed topology, which are different by finite size effects. Extending the work by Brower et al., we derive the formula to estimate these finite size corrections for arbitrary correlators in terms of the topological susceptibility and the theta dependence. Applying this formula, we show that topological susceptibility can be measured through two-point functions of pseudoscalar operator.

hep-lat↗

arXiv2007

Finite volume QCD at fixed topological charge

In finite volume the partition function of QCD with a given $θ$ is a sum of different topological sectors with a weight primarily determined by the topological susceptibility. If a physical observable is evaluated only in a fixed topological sector, the result deviates from the true expectation value by an amount proportional to the inverse space-time volume 1/V. Using the saddle point expansion, we derive formulas to express the correction due to the fixed topological charge in terms of a 1/V expansion. Applying this formula, we propose a class of methods to determine the topological susceptibility in QCD from various correlation functions calculated in a fixed topological sector.

hep-lat↗

arXiv2006

Heavy flavor physics from lattice QCD

I review the recent status of heavy flavor physics results from lattice QCD. In particular, I focus on the heavy-light decay constants, the bag parameters, the form factors, and the bottom quark mass. New progresses in theoretical methods are also reviewed.

hep-lat↗

arXiv2006

Improvement of algorithms for dynamical overlap fermions

We investigate the algorithms for dynamical overlap fermions aiming at improving the performance for large-scale simulations. We look for the best combination of Hybrid Monte Carlo options and iterative quark solvers with respect to the numerical costs. Our main target is a $N_f=2$ simulation with overlap fermion on a $16^3\times 32$ lattice at lattice spacing around 0.12 fm.

hep-lat↗

arXiv2005

Study of 1/m corrections in HQET

We report our exploratory study on the matching condition of HQET with QCD including 1/m corrections. We introduce a new observable from the dependence of the heavy-light effective energy on the twisted boundary condition parameter $θ$, which could be used to match the kinetic term $\vec{D}^2/(2m)$. Carrying out quenched QCD simulations for fixed lattice spacing in small volumes with O(a)-improved Wilson fermions, we study the 1/m dependence of this observable, from which the static limit and 1/m coefficient can be extracted. We also compare our preliminary result with HQET.

hep-lat↗

arXiv2005

Perturbative Study of the Supersymmetric Lattice Model from Matrix Model

We study the lattice model for the supersymmetric Yang-Mills theory in two dimensions proposed by Cohen, Kaplan, Katz, and Unsal. We re-examine the formal proof for the absence of susy breaking counter terms as well as the stability of the vacuum by an explicit perturbative calculation for the case of U(2) gauge group. Introducing fermion masses and treating the bosonic zero momentum mode nonperturbatively, we avoid the infra-red divergences in the perturbative calculation. As a result, we find that there appear mass counter terms for finite volume which vanish in the infinite volume limit so that the theory needs no fine-tuning.

hep-lat↗

arXiv2005

Search for the S=+1 pentaquarks in quenched lattice QCD

We study spin $\frac12$ hadronic states in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Our work is the first systematic lattice QCD study which properly carries out the following analyses: {\it (1) the careful extraction of the first two low energy states with very high statistics and the variational method} and {\it (2) the study of volume dependences of eigenenergies and spectral weights to distinguish resonance states from scattering states}. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $β$=5.7 with the standard plaquette gauge action and the Wilson quark action. Our result indicates the existence of a resonance state lying slightly above the NK threshold in $(I,J^P)=(0,\frac12^-)$ channel in quenched QCD.

hep-lat↗

arXiv2005

Perturbative Study of the Supersymmetric Lattice Theory from Matrix Model

hep-lat↗

arXiv2005

Search for the possible S=+1 Pentaquark states in Quenched Lattice QCD

We study spin $\frac12$ hadronic states in quenched lattice QCD to search for a possible $S=+1$ pentaquark resonance. Simulations are carried out on $8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices at $β$=5.7 at the quenched level with the standard plaquette gauge action and the Wilson quark action. We adopt a Dirichlet boundary condition in the time direction for the quark to circumvent the possible contaminations due to the (anti)periodic boundary condition for the quark field, which are peculiar to the pentaquark. By diagonalizing the $2\times 2$ correlation matrices constructed from two independent operators with the quantum numbers $(I,J)=(0,\frac12)$, we successfully obtain the energies of the lowest state and the 2nd-lowest state in this channel. The analysis of the volume dependence of the energies and spectral weight factors indicates that a resonance state is likely to exist slightly above the NK threshold in $(I,J^P)=(0,\frac12^-)$ channel.

hep-lat↗

arXiv2004

Application of heavy-quark effective theory to lattice QCD: II. Radiative corrections to heavy-light currents

We apply heavy-quark effective theory to separate long- and short-distance effects of heavy quarks in lattice gauge theory. In this approach, the inverse heavy-quark mass and the lattice spacing are treated as short distances, and their effects are lumped into short-distance coefficients. We show how to use this formalism to match lattice gauge theory to continuum QCD, order by order in the heavy-quark expansion. In this paper, we focus on heavy-light currents. In particular, we obtain one-loop results for the matching factors of lattice currents, needed for heavy-quark phenomenology, such as the calculation of heavy-light decay constants, and heavy-to-light transition form factors. Results for the Brodsky-Lepage-Mackenzie scale $q^*$ are also given.

hep-lat↗

arXiv2004

Anisotropic lattice with nonperturbative accuracy

We determine the nonperturbative anisotropic parameter of the gauge action in the quenched approximation with less than 1% accuracy using the Sommer scale measured by the Lüscher-Weisz algorithm or smearing technique. We also study the nonperturbative O(a)-improvement of the quark action. The bare quark anisotropy is determined using the masses from the temporal and spatial directions. For the determination of the $O(a)$ improvement coefficients, we apply the Schrödinger functional method.

hep-lat↗

arXiv2004

Theta vacuum effects on the pseudoscalar condensates and the eta^prime meson in 2-dimensional lattice QED

We study the chiral condensates and the eta^prime meson correlators of the massive Schwinger model in non-zero theta vacuum. Our data suggest that the pseudoscalar operator does condense in a fixed topological sector and gives long range correlations of the eta^prime meson. We find that this is well understood from the clustering decomposition and statistical picture. Our result also indicates that even in theta=0 case, the long range correlation of eta^prime meson receives non-zero contributions from all the topological sectors and that their cancellation is non-trivial and requires accurate measurement of the reweighting factors as well as the expectation values. It is then clear that the fluctuation of the disconnected diagram originates from the pseudoscalar condensates.

hep-lat↗

arXiv2004

A model independent determination of $|V_{ub}|$ using the global $q^2$ dependence of the dispersive bounds on the $B\toπlν$ form factors

We propose a method to determine the CKM matrix element $|V_{ub}|$ using the global $q^2$ dependence of the dispersive bound on the form factors for $B\to πlν$ decay. Since the lattice calculation of the $B\to πlν$ form factor is limited to the large $q^2$ regime, only the experimental data in a limited kinematic range can be used in a conventional method. In our new method which exploits the statistical distributions of the dispersive bound proposed by Lellouch, we can utilize the information of the global $q^2$ dependence for all kinematic range. As a feasibility study we determine $|V_{ub}|$ by combining the form factors from quenched lattice QCD, the dispersive bounds, and the experimental data by CLEO. We show that the accuracy of $|V_{ub}|$ can be improved by our method.

hep-lat↗