132 research outputs found
Mass dependence of the hairpin vertex in quenched QCD
The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a
key role in quenched chiral perturbation theory. Direct calculations using
lattice simulations find that it has a significant dependence on quark mass. I
show that this mass dependence can be used to determine the quenched
Gasser-Leutwyler constant L5. This complements the calculation of L5 using the
mass dependence of the axial decay constant of the pion. In an appendix, I
discuss power counting for quenched chiral perturbation theory and describe the
particular scheme used in this paper.Comment: 12 pages, 4 figures. Version to appear in Phys. Rev. D. Central
result unchanged, but explanation of calculation improved and minor errors
corrected. New appendix discusses power counting schemes in quenched chiral
perturbation theor
Partially quenched chiral perturbation theory without
This paper completes the argument that lattice simulations of partially
quenched QCD can provide quantitative information about QCD itself, with the
aid of partially quenched chiral perturbation theory. A barrier to doing this
has been the inclusion of , the partially quenched generalization of
the , in previous calculations in the partially quenched effective
theory. This invalidates the low energy perturbative expansion, gives rise to
many new unknown parameters, and makes it impossible to reliably calculate the
relation between the partially quenched theory and low energy QCD. We show that
it is straightforward and natural to formulate partially quenched chiral
perturbation theory without , and that the resulting theory contains
the effective theory for QCD without the . We also show that previous
results, obtained including , can be reinterpreted as applying to the
theory without . We contrast the situation with that in the quenched
effective theory, where we explain why it is necessary to include .
We also compare the derivation of chiral perturbation theory in partially
quenched QCD with the standard derivation in unquenched QCD. We find that the
former cannot be justified as rigorously as the latter, because of the absence
of a physical Hilbert space. Finally, we present an encouraging result:
unphysical double poles in certain correlation functions in partially quenched
chiral perturbation theory can be shown to be a property of the underlying
theory, given only the symmetries and some plausible assumptions.Comment: 45 pages, no figure
Unphysical Operators in Partially Quenched QCD
We point out that the chiral Lagrangian describing pseudo-Goldstone bosons in
partially quenched QCD has one more four-derivative operator than that for
unquenched QCD with three flavors. The new operator can be chosen to vanish in
the unquenched sector of the partially quenched theory. Its contributions begin
at next-to-leading order in the chiral expansion. At this order it contributes
only to unphysical scattering processes, and we work out some examples. Its
contributions to pseudo-Goldstone properties begin at next-to-next-to-leading
order, and we determine their form. We also determine all the zero and two
derivative operators in the partially quenched chiral Lagrangian,
finding three more than in unquenched QCD, and use these to give the general
form of the analytic next-to-next-to-leading order contributions to the
pseudo-Goldstone mass and decay constant. We discuss the general implications
of such additional operators for the utility of partially quenched simulationsComment: 13 pages, 11 figures Version 2: Additional footnote and parenthesis
in section
Hadronic Electromagnetic Properties at Finite Lattice Spacing
Electromagnetic properties of the octet mesons as well as the octet and
decuplet baryons are augmented in quenched and partially quenched chiral
perturbation theory to include O(a) corrections due to lattice discretization.
We present the results for the SU(3) flavor group in the isospin limit as well
as the results for SU(2) flavor with non-degenerate quarks. These corrections
will be useful for extrapolation of lattice calculations using Wilson valence
and sea quarks, as well as calculations using Wilson sea quarks and
Ginsparg-Wilson valence quarks.Comment: 19 pages, 0 figures, RevTeX
Nucleons Properties at Finite Lattice Spacing in Chiral Perturbation Theory
Properties of the proton and neutron are studied in partially-quenched chiral
perturbation theory at finite lattice spacing. Masses, magnetic moments, the
matrix elements of isovector twist-2 operators and axial-vector currents are
examined at the one-loop level in a double expansion in the light-quark masses
and the lattice spacing. This work will be useful in extrapolating the results
of simulations using Wilson valence and sea quarks, as well as simulations
using Wilson sea quarks and Ginsparg-Wilson valence quarks, to the continuum.Comment: 16 pages LaTe
Impact of the finite volume effects on the chiral behavior of fK and BK
We discuss the finite volume corrections to fK and BK by using the one-loop
chiral perturbation theory in full, quenched, and partially quenched QCD. We
show that the finite volume corrections to these quantities dominate the
physical (infinite volume) chiral logarithms.Comment: 16 pages, 3 figures [published version
Baryon Decuplet to Octet Electromagnetic Transitions in Quenched and Partially Quenched Chiral Perturbation Theory
We calculate baryon decuplet to octet electromagnetic transition form factors
in quenched and partially quenched chiral perturbation theory. We work in the
isospin limit of SU(3) flavor, up to next-to-leading order in the chiral
expansion, and to leading order in the heavy baryon expansion. Our results are
necessary for proper extrapolation of lattice calculations of these
transitions. We also derive expressions for the case of SU(2) flavor away from
the isospin limit.Comment: 16 pages, 3 figures, revtex
Simulations with different lattice Dirac operators for valence and sea quarks
We discuss simulations with different lattice Dirac operators for sea and
valence quarks. A goal of such a "mixed" action approach is to probe deeper the
chiral regime of QCD by enabling simulations with light valence quarks. This is
achieved by using chiral fermions as valence quarks while computationally
inexpensive fermions are used in the sea sector. Specifically, we consider
Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action
for this mixed theory is derived to O(a), and the appropriate low energy chiral
effective Lagrangian is constructed, including the leading O(a) contributions.
Using this Lagrangian one can calculate expressions for physical observables
and determine the Gasser-Leutwyler coefficients by fitting them to the lattice
data.Comment: 17 pages, 1 ps figure (2 clarification paragraphs added
Recommended from our members
Lattice calculations of electroweak decay amplitudes
I review the progress made during the last year in lattice calculations of weak and electromagnetic amplitudes. 32 refs., 9 figs., 2 tabs
How good is the quenched approximation of QCD?
The quenched approximation for QCD is, at present and in the foreseeable
future, unavoidable in lattice calculations with realistic choices of the
lattice spacing, volume and quark masses. In this talk, I review an analytic
study of the effects of quenching based on chiral perturbation theory. Quenched
chiral perturbation theory leads to quantitative insight on the difference
between quenched and unquenched QCD, and reveals clearly some of the diseases
which are expected to plague quenched QCD. Uses jnl.tex and epsf.tex for figure
3. Figures 1 and 2 not included, sorry. Available as hardcopy on request.Comment: 22 pages, Wash. U. HEP/94-62 (Forgotten set of macros now included,
sorry.
- …