arXiv subjects

Sinya Aoki

Publications and source records attributed to Sinya Aoki.

209 records · Page 12Linked to original sources

arXiv1998

One loop renormalization for the axial Ward-Takahashi identity in Domain-wall QCD

We calculate one-loop correction to the axial Ward-Takahashi identity given by Furman and Shamir in domain-wall QCD. It is shown perturbatively that the renormalized axial Ward-Takahashi identity is satisfied without fine tuning and the ``conserved'' axial current receives no renormalization, giving $Z_A=1$. This fact will simplify the calculation of the pion decay constant in numerical simulations since the decay constant defined by this current needs no lattice renormalization factor.

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

One-loop renormalization factors and mixing coeffecients of bilinear quark operators for improved gluon and quark actions

We calculate one-loop renormalization factors and mixing coefficients of bilinear quark operators for a class of gluon actions with six-link loops and O(a)-improved quark action. The calculation is carried out by evaluating on-shell Green's functions of quarks and gluons in the standard perturbation theory. We find a general trend that finite parts of one-loop coefficients are reduced approximately by a factor two for the renormalization-group improved gluon actions compared with the case of the standard plaquette gluon action.

hep-lat↗

arXiv1998

Computation of the improvement coefficient $c_{\rm sw}$ to 1-loop with improved gluon actions

The coefficient $c_{\rm sw}$ appearing in the Sheikholeslami-Wohlert improved action is computed to one loop perturbation theory for improved gluon actions including six-link loops. The O($a$) improvement coefficients for the dimension three isovector composite operators bilinear in the quark fields are also computed to one loop order of perturbation theory with degenerate non-vanishing quark masses.

hep-lat↗

arXiv1998

Perturbative Renormalization Factors of Bilinear Quark Operators for Improved Gluon and Quark Actions in Lattice QCD

We calculate one-loop renormalization factors of bilinear quark operators for gluon action including six-link loops and $O(a)$-improved quark action in the limit of massless quark. We find that finite parts of one-loop coefficients of renormalization factors diminish monotonically as either of the coefficients $c_1$ or $c_2+c_3$ of the six-link terms are decreased below zero. Detailed numerical results are given, for general values of the clover coefficient, for the tree-level improved gluon action in the Symanzik approach $(c_1=-1/12, c_2=c_3=0)$ and for the choices suggested by Wilson $(c_1=-0.252, c_2=0, c_3=-0.17)$ and by Iwasaki $(c_1=-0.331, c_2=c_3=0$ and $c_1=-0.27, c_2+c_3=-0.04)$ from renormalization-group analyses. Compared with the case of the standard plaquette gluon action, finite parts of one-loop coefficients are reduced by 10--20% for the Symanzik action, and approximately by a factor two for the renormalization-group improved gluon actions.

hep-lat↗

arXiv1996

Structure of Critical Lines in Quenched Lattice QCD with the Wilson Quark Action

The structure of critical lines of vanishing pion mass for the Wilson quark action is examined in quenched lattice QCD. The numerical evidence is presented that critical lines spread into five branches beyond beta=5.6-5.7 at zero temperature. It is also shown that critical lines disappear in the deconfined phase for the case of finite temperatures.

hep-lat↗

arXiv1992

Fermion mass in the Wilson-Yukawa approach for chiral Yukawa theory

We consider a modification of the Wilson-Yukawa model to overcome its difficulty that the fermion mass is not proportional to the Higgs vacuum expectation value. In the modification scalar and fermionic regulator fields are introduced so that all the physical fermion fields possess shift symmetry when the Yukawa coupling vanishes. With the fermionic hopping parameter expansion it is shown that the fermion mass is proportional to the Higgs vacuum expectation value and that the coupling of fermion to the external gauge field can be chiral if the hopping parameter of the scalar regulator field is taken to the critical value.

hep-lat↗

arXiv1992

A Study of the $N=2$ Kazakov-Migdal Model

We study numerically the SU(2) Kazakov-Migdal model of `induced QCD'. In contrast to our earlier work on the subject we have chosen here {\it not} to integrate out the gauge fields but to keep them in the Monte Carlo simulation. This allows us to measure observables associated with the gauge fields and thereby address the problem of the local $Z_2$ symmetry present in the model. We confirm our previous result that the model has a line of first order phase transitions terminating in a critical point. The adjoint plaquette has a clear discontinuity across the phase transition, whereas the plaquette in the fundamental representation is always zero in accordance with Elitzur's theorem. The density of small $Z_2$ monopoles shows very little variation and is always large. We also find that the model has extra local U(1) symmetries which do not exist in the case of the standard adjoint theory. As a result, we are able to show that two of the angles parameterizing the gauge field completely decouple from the theory and the continuum limit defined around the critical point can therefore not be `QCD'.

hep-lat↗

arXiv1992

Fermion Interactions in the Wilson Yukawa Approach for Lattice Chiral Gauge Theories

We consider fermion-gauge couplings in the Wilson-Yukawa approach for lattice chiral gauge theories. At the leading order of a fermionic hopping parameter expansion we find that the fermion-gauge coupling has a chiral and tree-like structure. We argue that this fermion-gauge coupling remains non-zero in the continuum limit taken in the Higgs phase. Possible fermion-scalar couplings in this approach are considered. We also evaluate the fermion interaction with an external gauge field in the slightly modified model and show that it has a chiral structure in general.

hep-lat↗

arXiv1992

Regularizations, Anomalies and Fermion Number Non-Conservation in Chiral Gauge Theories

We study how fermion number conservation fails in fermion number preserving regularization schemes. We show that the fermion number have to be carried by the gauge field configurations with non-zero winding number in this scheme and this fermion number is not conserved in the presence of instantons. We also consider other types of regularization scheme which have different global symmetries. In particular, we point out that the fermion number is conserved in the lattice chiral gauge theories with the Wilson-Yukawa coupling.

hep-lat↗

arXiv1992

On the Renormalization of the S Parameter

We calculate the S parameter of the standard model at one loop of fermions, using three different regularizations (dimensional, Pauli-Villars and lattice) and find an extra contribution to the S parameter besides the standard one for each case. This shows that the extra contribution recently reported for the lattice regularization is {\it not} necessarily tied to the non-decoupling effect of fermion doublers. We argue that the extra contribution should be subtracted in the renormalizable perturbative expansion.

hep-ph↗