1,294 research outputs found
Evidence for hard chiral logarithms in quenched lattice QCD
We present the first direct evidence that quenched QCD differs from full QCD
in the chiral () limit, as predicted by chiral perturbation
theory, from our quenched lattice QCD simulations at . We
measured the spectrum of light hadrons on ,
and , using staggered quarks of masses ,
and . The pion masses showed clear evidence for logarithmic
violations of the PCAC relation , as predicted by
quenched chiral perturbation theory. The dependence on spatial lattice volume
precludes this being a finite size effect. No evidence was seen for such chiral
logarithms in the behaviour of the chiral condensate
.Comment: 10 pages, 4 figures, uuencoded compressed postscript fil
Weak matrix elements for CP violation
We present preliminary results of matrix elements of four-fermion operators
relevant to the determination of e and e'/e using staggered fermions.Comment: 3 pages, 4 figures, Lattice 2001 (Hadronic Matrix Elements
Heavy-light and light-light weak matrix elements on the lattice
I review recent developments in lattice weak matrix element calculations. I
focus on on (both with propagating quarks and in the static limit for the
quark), semi-leptonic form factors for meson decay, form factors for , and . [Review presented at Lattice '93]Comment: 16 pages. (latex; 7 postscript figures included; 7 other figures are
reproduced from work by others and are not available here. Some hardcopies of
the talk will be available; send e-mail to [email protected].
Pion decay constant for the Kogut-Susskind quark action in quenched lattice QCD
We present a study for the pion decay constant in the quenched
approximation to lattice QCD with the Kogut-Susskind (KS) quark action, with
the emphasis given to the renormalization problems. Numerical simulations are
carried out at the couplings and 6.2 on and
lattices, respectively. The pion decay constant is evaluated
for all KS flavors via gauge invariant and non-invariant axial vector currents
with the renormalization constants calculated by both non-perturbative method
and perturbation theory. We obtain MeV in the continuum limit
as the best value using the partially conserved axial vector current, which
requires no renormalization. From a study for the other KS flavors we find that
the results obtained with the non-perturbative renormalization constants are
well convergent among the KS flavors in the continuum limit, confirming
restoration of flavor symmetry, while perturbative
renormalization still leaves an apparent flavor breaking effect even in the
continuum limit.Comment: LaTex, 27 pages, 35 eps figures, uses revtex and eps
Tables of Hyperonic Matter Equation of State for Core-Collapse Supernovae
We present sets of equation of state (EOS) of nuclear matter including
hyperons using an SU_f(3) extended relativistic mean field (RMF) model with a
wide coverage of density, temperature, and charge fraction for numerical
simulations of core collapse supernovae. Coupling constants of Sigma and Xi
hyperons with the sigma meson are determined to fit the hyperon potential
depths in nuclear matter, U_Sigma(rho_0) ~ +30 MeV and U_Xi(rho_0) ~ -15 MeV,
which are suggested from recent analyses of hyperon production reactions. At
low densities, the EOS of uniform matter is connected with the EOS by Shen et
al., in which formation of finite nuclei is included in the Thomas-Fermi
approximation. In the present EOS, the maximum mass of neutron stars decreases
from 2.17 M_sun (Ne mu) to 1.63 M_sun (NYe mu) when hyperons are included. In a
spherical, adiabatic collapse of a 15 star by the hydrodynamics
without neutrino transfer, hyperon effects are found to be small, since the
temperature and density do not reach the region of hyperon mixture, where the
hyperon fraction is above 1 % (T > 40 MeV or rho_B > 0.4 fm^{-3}).Comment: 23 pages, 6 figures (Fig.3 and related comments on pion potential are
corrected in v3.
Lattice QCD Calculation of the Kaon B-parameter with the Wilson Quark Action
The kaon B parameter is calculated in quenched lattice QCD with the Wilson
quark action. The mixing problem of the \Delta s=2 four-quark operators is
solved non-perturbatively with full use of chiral Ward identities, and this
method enables us to construct the weak four-quark operators exhibiting good
chiral behavior. We find B_K(NDR, 2GeV)=0.562(64) in the continuum limit, which
agrees with the value obtained with the Kogut-Susskind quark action.Comment: 11 pages, latex source-file, 4 figures as ps-fil
Applications of Partially Quenched Chiral Perturbation Theory
Partially quenched theories are theories in which the valence- and sea-quark
masses are different. In this paper we calculate the nonanalytic one-loop
corrections of some physical quantities: the chiral condensate, weak decay
constants, Goldstone boson masses, B_K and the K+ to pi+ pi0 decay amplitude,
using partially quenched chiral perturbation theory. Our results for weak decay
constants and masses agree with, and generalize, results of previous work by
Sharpe. We compare B_K and the K+ decay amplitude with their real-world values
in some examples. For the latter quantity, two other systematic effects that
plague lattice computations, namely, finite-volume effects and unphysical
values of the quark masses and pion external momenta are also considered. We
find that typical one-loop corrections can be substantial.Comment: 22 pages, TeX, refs. added, minor other changes, version to appear in
Phys. Rev.
Perturbative matching of staggered four-fermion operators with hypercubic fat links
We calculate the one-loop matching coefficients between continuum and lattice
four-fermion operators for lattice operators constructed using staggered
fermions and improved by the use of fattened links. In particular, we consider
hypercubic fat links and SU(3) projected Fat-7 links, and their mean-field
improved versions. We calculate only current-current diagrams, so that our
results apply for operators whose flavor structure does not allow
``eye-diagrams''. We present general formulae, based on two independent
approaches, and give numerical results for the cases in which the operators
have the taste (staggered flavor) of the pseudo-Goldstone pion. We find that
the one-loop corrections are reduced down to the 10-20% level, resolving the
problem of large perturbative corrections for staggered fermion calculations of
matrix elements.Comment: 37 pages, no figure, 20 table
One Spin Trace Formalism for
It has been known for some time that there are two methods to calculate with staggered fermions: one is the two spin trace formalism and the other is
the one spin trace formalism. Until now, the two spin trace formalism has been
exclusively used for weak matrix element calculations with staggered fermions.
Here, the one spin trace formalism to calculate with staggered fermions
is explained. It is shown that the one spin trace operators require additional
chiral partner operators in order to keep the continuum chiral behavior. The
renormalization of the one spin trace operators is described and compared with
the two spin trace formalism.Comment: 47 pages, latex, 4 figures are available on reques
Chiral perturbation theory for K+ to pi+ pi0 decay in the continuum and on the lattice
In this paper we use one-loop chiral perturbation theory in order to compare
lattice computations of the K+ to pi+ pi0 decay amplitude with the experimental
value. This makes it possible to investigate three systematic effects that
plague lattice computations: quenching, finite-volume effects, and the fact
that lattice computations have been done at unphysical values of the quark
masses and pion external momenta (only this latter effect shows up at tree
level). We apply our results to the most recent lattice computation, and find
that all three effects are substantial. We conclude that one-loop corrections
in chiral perturbation theory help in explaining the discrepancy between
lattice results and the real-world value. We also revisit B_K, which is closely
related to the K+ to pi+ pi0 decay amplitude by chiral symmetry.Comment: 50 pages, TeX, two eps figures included, minor changes, no changes in
results or conclusions, version to appear in Phys.Rev.
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