23 research outputs found
Unquenched quark propagator in Landau gauge
We present an unquenched calculation of the quark propagator in Landau gauge
with 2+1 flavors of dynamical quarks. We use configurations generated with an
improved staggered (``Asqtad'') action by the MILC collaboration. This quark
action has been seen to have excellent rotational symmetry and scaling
properties in the quenched quark propagator. Quenched and dynamical
calculations are performed on a lattice with a nominal lattice
spacing of fm. The matched quenched and dynamical lattices allow us
to investigate the relatively subtle sea quark effects, and even in the
quenched case the physical volume of these lattices gives access to lower
momenta than our previous study. We calculate the quark mass function and
renormalization function for a variety of valence and sea quark masses.Comment: 7 pages, 6 figure
Clones with finitely many relative R-classes
For each clone C on a set A there is an associated equivalence relation
analogous to Green's R-relation, which relates two operations on A iff each one
is a substitution instance of the other using operations from C. We study the
clones for which there are only finitely many relative R-classes.Comment: 41 pages; proofs improved, examples adde
Scaling behavior of quark propagator in full QCD
We study the scaling behavior of the quark propagator on two lattices with
similar physical volume in Landau gauge with 2+1 flavors of dynamical quarks in
order to test whether we are close to the continuum limit for these lattices.
We use configurations generated with an improved staggered (``Asqtad'') action
by the MILC collaboration. The calculations are performed on
lattices with lattice spacing fm and on lattices
with lattice spacing fm. We calculate the quark mass function,
, and the wave-function renormalization function, , for a
variety of bare quark masses. Comparing the behavior of these functions on the
two sets of lattices we find that both and show little
sensitivity to the ultraviolet cutoff.Comment: 6 pages, 5 figure
Scaling behavior and positivity violation of the gluon propagator in full QCD
The Landau-gauge gluon propagator is studied using the coarse and fine
dynamical MILC configurations. The effects of dynamical quarks are clearly
visible and lead to a reduction of the nonperturbative infrared enhancement
relative to the quenched case. Lattice spacing effects are studied and found to
be small. The gluon spectral function is shown to clearly violate positivity in
both quenched and full QCD.Comment: 7 pages, 9 figures. References and 1 figure added, minor text
modifications, version to be published in PR
From Euclidean to Minkowski space with the Cauchy-Riemann equations
We present an elementary method to obtain Green's functions in
non-perturbative quantum field theory in Minkowski space from calculated
Green's functions in Euclidean space. Since in non-perturbative field theory
the analytical structure of amplitudes is many times unknown, especially in the
presence of confined fields, dispersive representations suffer from systematic
uncertainties. Therefore we suggest to use the Cauchy-Riemann equations, that
perform the analytical continuation without assuming global information on the
function in the entire complex plane, only in the region through which the
equations are solved. We use as example the quark propagator in Landau gauge
Quantum Chromodynamics, that is known from lattice and Dyson-Schwinger studies
in Euclidean space. The drawback of the method is the instability of the
Cauchy-Riemann equations to high-frequency noise, that makes difficult to
achieve good accuracy. We also point out a few curiosities related to the Wick
rotation.Comment: 12 pages in EPJ double-column format, 16 figures. This version: added
paragraph, two reference
Renormalizability of a quark-gluon model with soft BRST breaking in the infrared region
We prove the renormalizability of a quark-gluon model with a soft breaking of
the BRST symmetry, which accounts for the modification of the large distance
behavior of the quark and gluon correlation functions. The proof is valid to
all orders of perturbation theory, by making use of softly broken Ward
identities.Comment: 20 pages, no figures. Preprint number added in v2
Effects of dynamical sea-quarks on quark and gluon propagators
We present an unquenched calculation of the quark propagator in Landau gauge with 2+1 flavors of dynamical quarks. We study the scaling behavior of the quark propagator in full QCD on two lattices with different lattice spacings and similar physical volume. We use configurations generated with an improved staggered ("Asqtad") action by the MILC collaboration. © 2006 American Institute of Physics.Maria B. Parappilly, Patrick O. Bowman, Urs M. Heller, Derek B. Leinweber, Anthony G. Williams, and J. B. Zhan
Phase diagrams in nonlocal PNJL models constrained by Lattice QCD results
Based on lattice QCD-adjusted SU(2) nonlocal Polyakov--Nambu--Jona-Lasinio
(PNJL) models, we investigate how the location of the critical endpoint in the
QCD phase diagram depends on the strenght of the vector meson coupling, as well
as the Polyakov-loop (PL) potential and the form factors of the covariant
model. The latter are constrained by lattice QCD data for the quark propagator.
The strength of the vector coupling is adjusted such as to reproduce the slope
of the pseudocritical temperature for the chiral phase transition at low
chemical potential extracted recently from lattice QCD simulations. Our study
supports the existence of a critical endpoint in the QCD phase diagram albeit
the constraint for the vector coupling shifts its location to lower
temperatures and higher baryochemical potentials than in the case without it.Comment: 23 pages, 10 figures. Version accepted in Phys. Part. Nucl. Lett. (to
appear), references adde
The chiral and angular momentum content of the rho-meson
It is possible to define and calculate in a gauge-invariant manner the chiral
as well as the partial wave content of the quark-antiquark Fock component of a
meson in the infrared, where mass is generated. Using the variational method
and a set of interpolators that span a complete chiral basis we extract in a
lattice QCD Monte Carlo simulation with two dynamical light quarks the orbital
angular momentum and spin content of the rho-meson. We obtain in the infrared a
simple 3S1 component as a leading component of the rho-meson with a small
admixture of the 3D1 partial wave, in agreement with the SU(6) flavor-spin
symmetry.Comment: 23 pages, 4 figures, 2 table
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We review the infrared properties of the pure Yang-Mills correlators and
discuss recent results concerning the two classes of low-momentum solutions for
them reported in literature; i.e. decoupling and scaling solutions. We will
mainly focuss on the Landau gauge and pay special attention to the results
inferred from the analysis of the Dyson-Schwinger equations of the theory and
from "{\it quenched}" lattice QCD. The results obtained from properly
interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs