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T. Izubuchi

Publications and source records attributed to T. Izubuchi.

At least 73 records · Page 4Linked to original sources
arXiv2004

Scalar meson in dynamical and partially quenched two-flavor QCD: lattice results and chiral loops

This is an exploratory study of the lightest non-singlet scalar $q\bar q$ state on the lattice with two dynamical quarks. Domain Wall fermions are used for both sea and valence quarks on a 16^3*32 lattice with an inverse lattice spacing of 1.7 GeV. We extract the scalar meson mass 1.58(34) GeV from the exponential time-dependence of the dynamical correlators with $m_{val}=m_{sea}$ and N_f=2. Since this statistical error-bar from dynamical correlators is rather large, we analyze also the partially quenched lattice correlators with $m_{val}$ not equal $m_{sea}$. They are positive for $m_{val}>=m_{sea}$ and negative for $m_{val} =m_{sea}$ and negative for $m_{val}<m_{sea}$ at large t. After the subtraction of this unphysical contribution from the partially quenched lattice correlators, the correlators are positive and exponentially falling. The resulting scalar meson mass 1.51(19) GeV from the partially quenched correlators is consistent with the dynamical result and has appreciably smaller error-bar.

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

Domain wall fermions with improved gauge actions

We study the chiral properties of quenched domain wall fermions with several gauge actions. We demonstrate that the residual chiral symmetry breaking, which is present for a finite number of lattice sites in the fifth dimension ($L_s$), can be substantially suppressed using improved gauge actions. In particular the Symanzik action, the Iwasaki action, and a renormalization group improved gauge action, called doubly blocked Wilson (DBW2), are studied and compared to the Wilson action. All improved gauge actions studied show a reduction in the additive residual quark mass, $\mres$. Remarkably, in the DBW2 case $\mres$ is roughly two orders of magnitude smaller than the Wilson gauge action at $a^{-1}=2$ GeV and $L_s=16$. Significant reduction in $\mres$ is also realized at stronger gauge coupling corresponding to $a^{-1}=1.3$ GeV. As our numerical investigation indicates, this reduction is achieved by reducing the number of topological lattice dislocations present in the gauge field configurations. We also present detailed results for the quenched light hadron spectrum and the pion decay constant using the DBW2 gauge action.

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arXiv2001

Chiral property of domain-wall fermion from eigenvalues of 4D Wilson-Dirac Operator

We investigate a chiral property of the domain-wall fermion (DWF) system using the four-dimensional hermitian Wilson-Dirac operator $H_W$. A formula expressing the Ward-Takahashi identity quark mass $m_{5q}$ with eigenvalues of this operator is derived, which well explains the $N_5$ dependence of $m_{5q}$ observed in previous numerical simulations. We further discuss the chiral property of DWF in the large volume in terms of the spectra of $H_W$.

hep-lat↗
arXiv2001

Calculation of $K\toππ$ decay amplitudes from $K\toπ$ matrix elements in quenched domain-wall QCD

We present a calculation of the $K\toππ$ decay amplitudes from the $K\toπ$ matrix elements using leading order relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD with the domain-wall fermion action and the renormalization group improved gluon action. Our results show that the I=2 amplitude is reasonably consistent with experiment whereas the I=0 amplitude is sizably smaller. Consequently the $ΔI=1/2$ enhancement is only half of the experimental value, and $ε'/ε$ is negative.

hep-lat↗
arXiv2001

Kaon B parameter from quenched domain-wall QCD

We report on a calculation of $B_K$ with domain wall fermion action in quenched QCD. Simulations are made with a renormalization group improved gauge action at $β=2.6$ and 2.9 corresponding to $a^{-1}\approx 2$GeV and 3GeV. Effects due to finite fifth dimensional size $N_5$ and finite spatial size $N_σ$ are examined in detail. Matching to the continuum operator is made perturbatively at one loop order. We obtain $B_K(μ= 2 GeV)= 0.5746(61)(191)$, where the first error is statistical and the second error represents an estimate of scaling violation and ${\cal O}(α^2)$ errors in the renormalization factor added in quadrature, as an estimate of the continuum value in the $\msbar$ scheme with naive dimensional regularization. This value is consistent, albeit somewhat small, with $B_K(μ= 2 {GeV})= 0.628(42)$ obtained by the JLQCD Collaboration using the Kogut-Susskind quark action. Results for light quark masses are also reported.

hep-lat↗
arXiv2000

Eigenvalues of the hermitian Wilson-Dirac operator and chiral properties of the domain-wall fermion

Chiral properties of QCD formulated with the domain-wall fermion (DWQCD) are studied using the anomalous quark mass m_{5q} and the spectrum of the 4-dimensional Wilson-Dirac operator. Numerical simulations are made with the standard plaquette gauge action and a renormalization-group improved gauge action. Results are reported on the density of zero eigenvalue obtained with the accumulation method, and a comparison is made with the results for m_{5q}.

hep-lat↗
arXiv2000

Calculation of $K\to π$ matrix elements in quenched domain-wall QCD

We explore the possibility for an evaluation of non-leptonic $ΔS=1$ $K$ decay amplitudes through the calculation of $K\toπ$ matrix elements using domain-wall QCD. The relation between the physical $K\toππ$ matrix elements and $K\toπ$ matrix elements deduced from chiral perturbation theory is recapitulated. Quenched numerical simulations are performed on an $16^3\times 32\times 16$ lattice at a lattice spacing $a^{-1}\approx 2$GeV for both the standard plaquette gauge action and a renormalization-group improved gauge action, and reasonable signals for $K\toπ$ matrix elements are obtained. Preliminary results are reported on the $K\toππ$ matrix elements, and results from two actions are compared.

hep-lat↗
arXiv2000

Kaon B parameter from quenched domain-wall QCD

We report on a calculation of $B_K$ with domain wall fermion action in quenched QCD. Simulations are made with a renormalization group improved gauge action at $β=2.6$ and 2.9 corresponding to $a^{-1}\approx 2$GeV and 3GeV. Effects due to finite fifth dimensional size $N_5$ and finite spatial size $N_σ$ are examined in detail. Matching to the continuum operator is made perturbatively at one loop order. We obtain $B_K(μ= 2 {GeV})= 0.5746(61)$, where the error is statistical only, as an estimate of the continuum value in the $\msbar$ scheme with naive dimensional regularization. This value is smaller but consistent with $B_K(μ= 2 {GeV})= 0.628(42)$ obtained by the JLQCD Collaboration using the Kogut-Susskind quark action. Results for strange quark mass are also reported.

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↗
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

Quenched QCD with domain-wall fermions on coarse lattices

We investigate the existence of chiral zero modes at a^{-1} \simeq 1 GeV in quenched domain-wall QCD. Simulations are carried out for the plaquette and an RG-improved gauge actions on a 12^3x24xN_s lattice with N_s=10-50. We find that the pion mass in the chiral limit remains non-vanishing as N_s\to\infty for both gauge actions. Possible origins of this non-vanishing pion mass are discussed.

hep-lat↗
arXiv1997

Single massless Majorana fermion in the domain-wall formalism

We study the domain-wall formalism with additional Majorana mass term for the unwanted zero mode, which has recently been proposed for lattice construction of 4D N=1 super Yang-Mills theory without fine-tuning. Switching off the gauge field, we study the dispersion relation of the energy eigenstates numerically, and find that the method works for reasonable values of Majorana mass. We point out, however, that a problem arises for too large Majorana mass, which can be understood in terms of the seesaw mechanism.

hep-lat↗
arXiv1997

A new phase structure in three-dimensional dynamical triangulation model

We investigate a new phase structure of the three-dimensional dynamical triangulation model with an additional local term by Monte Carlo simulation. We find that the first order phase transition observed for the naive Einstein-Hilbert action terminates at a finite coefficient of the new term. The phase transition turns into second order at the endpoint, beyond which it becomes a crossover.

hep-lat↗
arXiv1997

Massless Majorana fermion on the domain wall

We study the domain-wall formalism with additional Majorana mass term for the unwanted zero mode, which has recently been proposed for lattice construction of 4D N=1 super Yang-Mills theory without fine-tuning. Switching off the gauge field, we study the dispersion relation of the energy eigenstates numerically, and find that the method works for reasonable values of Majorana mass. We point out, however, that a problem arises for too large Majorana mass, which can be understood in terms of the seesaw mechanism.

hep-lat↗
arXiv1997

Singular Vertices in the Strong Coupling Phase of Four-Dimensional Simplicial Gravity

We study four-dimensional simplicial gravity through numerical simulation with special attention to the existence of singular vertices, in the strong coupling phase, that are shared by abnormally large numbers of four-simplices. We attempt to cure this disease by adding a term to the action which suppresses such singular vertices. For a sufficiently large coefficient of the additional term, however, the phase transition disappears and the system is observed to be always in the branched polymer phase for any gravitational constant.

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