arXiv subjects

Yoshinobu Kuramashi

Publications and source records attributed to Yoshinobu Kuramashi.

At least 109 records · Page 6Linked to original sources

arXiv2004

Perturbative determination of mass dependent renormalization and improvement coefficients for the heavy-light vector and axial-vector currents with relativistic heavy and domain-wall light quarks

We determine the mass dependent renormalization as well as improvement coefficients for the heavy-light vector and axial-vector currents consisting of the relativistic heavy and the domain-wall light quarks through the standard matching procedure. The calculation is carried out perturbatively at the one loop level to remove the systematic error of $O(α_s (am_Q)^n a\p)$ as well as $O(α_s (am_Q)^n)$ ($n\ge$0), where $\p$ is a typical momentum scale in the heavy-light system. We point out that renormalization and improvement coefficients of the heavy-light vector current agree with those of the axial-vector current, thanks to the exact chiral symmetry for the light quark. The results obtained with three different gauge actions, plaquette, Iwasaki and DBW2, are presented as a function of heavy quark mass and domain-wall height.

hep-lat↗

arXiv2004

Perturbative Determination of Mass Dependent $O(a)$ Improvement Coefficients for the Vector and Axial Vector Currents with a Relativistic Heavy Quark Action

We carry out a perturbative determination of mass dependent renormalization factors and $O(a)$ improvement coefficients for the vector and axial vector currents with a relativistic heavy quark action, which we have designed to control $m_Qa$ errors by extending the on-shell $O(a)$ improvement program to the case of $m_Q \gg Λ_{\rm QCD}$ with $m_Q$ the heavy quark mass. We discuss what kind of improvement operators are required for the heavy-heavy and the heavy-light cases under the condition that the Euclidean rotational symmetry is not retained anymore because of the $m_Qa$ corrections. Our calculation is performed employing the ordinary perturbation theory with the fictitious gluon mass as an infrared regulator. We show that all the improvement coefficients are determined free from infrared divergences. Results of the renormalization factors and the improvement coefficients are presented as a function of $m_Q a$ for various improved gauge actions as well as the plaquette action.

hep-lat↗

arXiv2003

One-loop calculation of mass dependent ${\cal O}(a)$ improvement coefficients for the relativistic heavy quarks on the lattice

We carry out the one-loop calculation of mass dependent ${\cal O}(a)$ improvement coefficients in the relativistic heavy quark action recently proposed, employing the ordinary perturbation theory with the fictitious gluon mass as an infrared regulator. We also determine renormalization factors and improvement coefficients for the axial-vector current at the one-loop level. It is shown that the improvement coefficients are infrared finite at the one-loop level if and only if the improvement coefficients in the action are properly tuned at the tree level.

hep-lat↗

arXiv2003

A Perturbative Determination of Mass Dependent $O(a)$ Improvement Coefficients in a Relativistic Heavy Quark Action

We present the results for a perturbative determination of mass dependent improvement coefficients $ν$, $r_s$, $c_E$ and $c_B$ in a relativistic heavy quark action, which we have designed to control $m_Qa$ errors by extending the on-shell $O(a)$ improvement program to the case of $m_Q \gg Λ_{\rm QCD}$, where $m_Q$ is the heavy quark mass. The parameters $ν$ and $r_s$ are determined from the quark propagator and $c_E$ and $c_B$ are from the on-shell quark-quark scattering amplitude. We show that all the parameters, together with the quark wave function and the mass renormalization factors, are determined free from infrared divergences once their tree level values are properly tuned. Results of these parameters are shown as a function of $m_Q a$ for various improved gauge actions.

hep-lat↗

arXiv2003

The Lattice $Λ$ Parameter in Domain Wall QCD

We evaluate the ratio of the scale parameter $Λ$ in domain wall QCD to the one in the continuum theory at one loop level incorporating the effect of massless quarks. We show that the Pauli-Villars regulator is required to subtract the unphysical massive fermion modes which emerge in the fermion loop contributions to the gluon self energy. Detailed results are presented as a function of the domain wall height $M$.

hep-lat↗

arXiv2003

Determination of the Improvement Coefficient c_SW up to One-Loop Order with the Conventional Perturbation Theory

We calculate the $O(a)$ improvement coefficient c_SW in the Sheikholeslami-Wohlert quark action for various improved gauge actions with six-link loops. We employ the conventional perturbation theory introducing the fictitious gluon mass to regularize the infrared divergence. Our results for some improved gauge actions are in agreement with those previously obtained with the Schr{ö}dinger functional method.

hep-lat↗

arXiv2002

Perturbative renormalization factors in domain-wall QCD with improved gauge actions

We evaluate renormalization factors of the domain-wall fermion system with various improved gauge actions at one loop level. The renormalization factors are calculated for quark wave function, quark mass, bilinear quark operators, three- and four-quark operators in modified minimal subtraction (MS-bar) scheme with the dimensional reduction(DRED) as well as the naive dimensional regularization(NDR). We also present detailed results in the mean field improved perturbation theory.

hep-lat↗

arXiv2001

Relativistic heavy quarks on the lattice

We investigate feasibility of relativistic approaches to the heavy quark physics on both anisotropic and isotropic lattices. Our peturbative calculation reveals that the anisotropic lattice is not theoretically adovantageous over the isotropic one to control $m_Q a$ errors. We instead propose a new relativistic approach to handle heavy quarks on the isotropic lattice.

hep-lat↗

arXiv2001

Relativistic Heavy Quarks on the Lattice

Lattice QCD should allow quantitative predictions for the heavy quark physics from first principles. Up to now, however, most approaches have based on the nonrelativistic effective theory, with which the continuum limit can not be taken in principle. In this paper we investigate feasibility of relativistic approaches to the heavy quark physics in lattice QCD. We first examine validity of the idea that the use of the anisotropic lattice could be advantageous to control the $m_Q a$ corrections. Our perturbative calculation, however, reveals that this is not true. We instead propose a new relativistic approach to handle heavy quarks on the isotropic lattice. We explain how power corrections of $m_Q a$ can be avoided and remaining uncertainties are reduced to be of order $(aΛ_{QCD})^2$.

hep-lat↗

arXiv2001

Nucleon Decay Matrix Elements from Lattice QCD

We present a GUT-model-independent calculation of hadron matrix elements for all dimension-six operators associated with baryon number violating processes using lattice QCD. Our results cover all the matrix elements required to estimate the partial lifetimes of (proton,neutron)$\to$($π,K,η$) +(${\bar ν},e^+,μ^+$) decay modes. We point out the necessity of disentangling two form factors that contribute to the matrix elements; previous calculations did not make the separation, which led to an underestimate of the physical matrix elements. With a correct separation, we find that the matrix elements have values 3-5 times larger than the smallest estimates employed in phenomenological analyses of the nucleon decays, which gives stronger constraints on GUT models. We also find that the values of the matrix elements are comparable with the tree-level predictions of chiral Lagrangian.

hep-ph↗

arXiv2000

Perturbative renormalization factors of $ΔS = 1$ four-quark operators for domain-wall QCD

Renormalization factors for $ΔS =1$ four-quark operators in the effective weak Hamiltonian are perturbatively evaluated in domain-wall QCD. The one-loop corrections of $ΔS=1$ four-quark operators consist of two types of diagrams: one is gluon exchange between quark lines and the other is penguin diagrams containing quark loops. Combining both contributions, our results allow a lattice calculation of the amplitude for $K\to ππ$ decays with $O(g^2)$ corrections included.

hep-lat↗

arXiv2000

Domain Wall Fermions in Quenched Lattice QCD

We study the chiral properties and the validity of perturbation theory for domain wall fermions in quenched lattice QCD at beta=6.0. The explicit chiral symmetry breaking term in the axial Ward-Takahashi identity is found to be very small already at Ns=10, where Ns is the size of the fifth dimension, and its behavior seems consistent with an exponential decay in Ns within the limited range of Ns we explore. From the fact that the critical quark mass, at which the pion mass vanishes as in the case of the ordinary Wilson-type fermion, exists at finite Ns, we point out that this may be a signal of the parity broken phase and investigate the possible existence of such a phase in this model at finite Ns. The rho and pi meson decay constants obtained from the four-dimensional local currents with the one-loop renormalization factor show a good agreement with those obtained from the conserved currents.

hep-lat↗

arXiv1999

Light Hadron Weak Matrix Elements

Recent developments in lattice QCD calculation of weak matrix elements involving light quarks are described. We focus on four topics: $B_K$ with the Kogut-Susskind and Wilson quark actions, $ΔI=1/2$ rule, proton decay matrix elements and the application of domain wall QCD to calculation of weak matrix elements.

hep-lat↗

arXiv1999

Perturbative renormalization factors of quark operators for domain-wall QCD

We calculate one-loop renormalization factors of several quark operators including bilinear, three- and four-quark operator for domain-wall fermion action. Since Green functions are constructed for external physical quark fields, our renormalization method is simple and can be easily applied to calculation of any quark operators. Our results show that these renormalized quark operators preserve several chiral properties of continuum massless QCD, which can be understood by the property of external quark line propagator.

hep-lat↗

arXiv1999

CP-PACS results for light hadron spectrum in quenched and two-flavor full QCD

We present a summary of our results for the light hadron spectrum in quenched lattice QCD and preliminary ones in two-flavor full QCD. For the quenched hadron spectrum we find that the mass formulae predicted by quenched chiral perturbation theory(QChPT) give a good description of our results. Employing the QChPT mass formulae for chiral extrapolations we conclude that the mass spectrum in the continuum limit deviates unambiguously and systematically from experiment. For our two-flavor full QCD results we focus on the dynamical quark effects on the light hadron spectrum.

hep-lat↗

arXiv1999

Perturbative renormalization factors of three- and four-quark operators for domain-wall QCD

Renormalization factors for three- and four-quark operators, which appear in the low energy effective Lagrangian of the proton decay and the weak interactions, are perturbatively calculated in domain-wall QCD. We find that the operators are multiplicatively renormalizable up to one-loop level without mixing with any other operators that have different chiral structures. As an application, we evaluate a renormalization factor for $B_K$ at the parameters where previous simulations have been performed, and find one-loop corrections to $B_K$ are 1-5% in these cases.

hep-lat↗

arXiv1998

Perturbative Renormalization Factors of Quark Bilinear Operators for Domain-wall QCD

We calculate one-loop renormalization factors of bilinear operators made of physical quark fields for domain-wall QCD. We find that finite parts of such renormalization factors have reasonable values at 1-loop except an overlap factor between the physical quark field and the zero mode in the theory. We point out that the 1-loop estimate of overall renormalization factors becomes unreliable at the coupling where numerical simulations are currently performed, due to the presence of this overlap factor. We show that this problem disappears if the mean-field improved perturbation theory is employed for renormalization factors.

hep-lat↗

arXiv1998

Perturbative Renormalization Factors of Bilinear Operators for Massive Wilson Quarks on the Lattice

Renormalization factors for local vector and axial vector currents for the Wilson quark action are perturbatively calculated to one loop order including finite quark masses from the ratio of the on-shell quark matrix elements in the Feynman gauge defined on the lattice and in the continuum. For large quark masses of order unity in lattice units, we find that finite quark mass effects are quite large: one-loop coefficients of the renormalization factors differ by 100% compared to those in the massless limit.

hep-lat↗