Eigo Shintani

Lattice study of infrared behaviour in SU(3) gauge theory with twelve massless flavours

A bstractWe present details of a lattice study of infrared behaviour in SU(3) gauge theory with twelve massless fermions in the fundamental representation. Using the step-scaling method, we compute the coupling constant in this theory over a large range of scale. The renormalisation scheme in this work is defined by the ratio of Polyakov loop correlators in the directions with different boundary conditions. We closely examine systematic effects, and find that they are dominated by errors arising from the continuum extrapolation. Our investigation suggests that SU(3) gauge theory with twelve flavours contains an infrared fixed point.

Two-Photon Decay of the Neutral Pion in Lattice QCD

We perform a nonperturbative calculation of the π(0) → γγ transition form factor and the associated decay width using lattice QCD. The amplitude for a two-photon final state, which is not an eigenstate of QCD, is extracted through a Euclidean time integral of the relevant three-point function. We utilize the all-to-all quark propagator technique to carry out this integration as well as to include the disconnected quark diagram contributions. The overlap fermion formulation is employed on the lattice to ensure exact chiral symmetry on the lattice. After examining various sources of systematic effects, except for a possible discretization effect, we obtain Γπ(0) → γγ = 7.83(31)(49) eV for the pion decay width, where the first error is statistical and the second is our estimate of the systematic error.

Study of the scaling properties in SU(2) gauge theory with eight flavors

We present our preliminary study of the SU(2) gauge theory with 8 flavors of fermions in fundamental representation. This theory could be a candidate of the gauge theory with conformal fixed point. By using Wilson/Polyakov loop in a finite volume with twisted boundary conditions, we study the renormalization group flow of the gauge coupling constant. Our calculation gives consistent result with the perturbative prediction of the running coupling in the weak coupling region. We investigate a possible signal for conformal behavior in the strong coupling region.

Erratum: Strong coupling constant from vacuum polarization functions in three-flavor lattice QCD with dynamical overlap fermions [Phys. Rev. D 82, 074505 (2010)]

In our analysis published in our paper, we found an error in the code to convert the strong coupling constant obtained by lattice QCD on Nf 1⁄4 2þ 1 at 2 GeV to that in Nf 1⁄4 5 at the MZ scale using the next-to-leading order in the MS scheme [1]. The central value as well as the systematic error is modified from Table I in our paper to Table I. The final value of αð5Þ s ðMZÞ in the Abstract and Eq. (17) in our paper should be changed to αð5Þ s ðMZÞ 1⁄4 0.1118ð3Þ þ16 −17 : (1)

Position space formulation for Dirac fermions on honeycomb lattice

Abstract We study how to construct Dirac fermion defined on the honeycomb lattice in position space. Starting from the nearest neighbor interaction in tight binding model, we show that the Hamiltonian is constructed by kinetic term and second derivative term of three flavor Dirac fermions in which one flavor has a mass of cutoff order and the other flavors are massless. In this formulation, the structure of the Dirac point is simplified so that its uniqueness can be easily shown even if we consider the next-to-nearest neighbor interaction. We also show that there is a hidden exact U ( 1 ) symmetry (flavor–chiral symmetry) at finite lattice spacing, which protects the masslessness of the Dirac fermion, and discuss the analogy with the staggered fermion formulation.

Search for the IR fixed point in the Twisted Polyakov Loop scheme (II)

We measure the renormalized coupling in the Twisted Polyakov loop scheme for SU(3) gauge theory coupled with

Nucleon sigma term and strange quark content in 2+1-flavor QCD with dynamical overlap fermions

N_f=12

Strong coupling constant from vacuum polarization functions in three-flavor lattice QCD with dynamical overlap fermions

fundamental fermions. To find the infrared fixed point of this theory, we focus on the step scaling function for the renormalized coupling. We take the continuum limit using the linear function of

Simulation of quantum chromodynamics on the lattice with exactly chiral lattice fermions

(a/L)^2

Topological susceptibility and axial symmetry at finite temperature

and a constant fit function. We find that there is a sizeable systematic error due to the choice of the continuum extrapolation function in the low energy region. We will give some directions to reduce the systematic errors.