423 research outputs found
Non--perturbative tests of the fixed point action for SU(3) gauge theory
In this paper (the second of a series) we extend our calculation of a
classical fixed point action for lattice pure gauge theory to include
gauge configurations with large fluctuations. The action is parameterized in
terms of closed loops of link variables. We construct a few-parameter
approximation to the classical FP action which is valid for short correlation
lengths. We perform a scaling test of the action by computing the quantity where the string tension is measured from the
torelon mass . We measure on lattices of fixed physical
volume and varying lattice spacing (which we define through the
deconfinement temperature). While the Wilson action shows scaling violations of
about ten per cent, the approximate fixed point action scales within the
statistical errors for . Similar behaviour is found for
the potential measured in a fixed physical volume.Comment: 28 pages (latex) + 11 figures (Postscript), uuencode
First results from a parametrized Fixed-Point QCD action
We have constructed a new fermion action which is an approximation to the
(chirally symmetric) Fixed-Point action, containing the full Clifford algebra
with couplings inside a hypercube and paths built from renormalization group
inspired fat links. We present an exploratory study of the light hadron
spectrum and the energy-momentum dispersion relation.Comment: Lattice2001(improvement), 3 pages, based on a talk by S.H; reference
update
Progress using generalized lattice Dirac operators to parametrize the Fixed-Point QCD action
We report on an ongoing project to parametrize the Fixed-Point Dirac operator
for massless quarks, using a very general construction which has arbitrarily
many fermion offsets and gauge paths, the complete Clifford algebra and
satisfies all required symmetries. Optimizing a specific construction with
hypercubic fermion offsets, we present some preliminary results.Comment: Lattice 2000 (Improvement), 9 pages, based on a talk by K.H. and a
poster by T.J. References adde
The construction of generalized Dirac operators on the lattice
We discuss the steps to construct Dirac operators which have arbitrary
fermion offsets, gauge paths, a general structure in Dirac space and satisfy
the basic symmetries (gauge symmetry, hermiticity condition, charge
conjugation, hypercubic rotations and reflections) on the lattice. We give an
extensive set of examples and offer help to add further structures.Comment: 19 pages, latex, maple code attache
Factorization of Fermion Doubles on the Lattice
We address the problem of the fermion species doubling on the Lattice. Our
strategy is to factorize the fermion doubles from the action. The mass term of
the Dirac-Wilson action is changed. In this case the extra roots which appear
in the action of free fermions in the moment representation are independent of
the mass and can be factorized from the fermion propagator. However the gauge
couplings suffer from the pathological ghost poles which are common to
non-local actions. This action can be used to find a solution of the Ginsparg
Wilson relation, which is cured from the non-local pathology. Finally we
compare this factorized action with solutions of The Ginsparg Wilson relation.
We find that the present is equivalent to the Zenkin action, and that is not
quite as local as the Neuberger action.Comment: 7 Latex Revtex pages, 4 ps figures. The paper was improoved due to
Comments received. It has a new section and several new reference
Chiral measurements with the Fixed-Point Dirac operator and construction of chiral currents
In this preliminary study, we examine the chiral properties of the
parametrized Fixed-Point Dirac operator D^FP, see how to improve its chirality
via the Overlap construction, measure the renormalized quark condensate Sigma
and the topological susceptibility chi_t, and investigate local chirality of
near zero modes of the Dirac operator. We also give a general construction of
chiral currents and densities for chiral lattice actions.Comment: Lattice2001(chiral), based on a talk by T.J. and a poster by K.H., 6
page
Instanton classical solutions of SU(3) fixed point actions on open lattices
We construct instanton-like classical solutions of the fixed point action of
a suitable renormalization group transformation for the SU(3) lattice gauge
theory. The problem of the non-existence of one-instantons on a lattice with
periodic boundary conditions is circumvented by working on open lattices. We
consider instanton solutions for values of the size (0.6-1.9 in lattice units)
which are relevant when studying the SU(3) topology on coarse lattices using
fixed point actions. We show how these instanton configurations on open
lattices can be taken into account when determining a few-couplings
parametrization of the fixed point action.Comment: 23 pages, LaTeX, 4 eps figures, epsfig.sty; some comments adde
Fixed-point action for fermions in QCD
We report our progress constructing a fixed-point action for fermions
interacting with SU(3) gauge fields.Comment: 3 pages, LaTeX file. Talk presented at LATTICE96(improvement
Fragmentation is crucial for the steady-state dynamics of actin filaments
Despite the recognition that actin filaments are important for numerous cellular processes, and decades of investigation, the dynamics of in vitro actin filaments are still not completely understood. Here, we follow the time evolution of the length distribution of labeled actin reporter filaments in an unlabeled F-actin solution via fluorescence microscopy. Whereas treadmilling and diffusive length fluctuations cannot account for the observed dynamics, our results suggest that at low salt conditions, spontaneous fragmentation is crucial
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