114 research outputs found
Lattice QCD without tuning, mixing and current renormalization
The classically perfect action of QCD requires no tuning to get the pion
massless in the broken phase: the critical bare mass is zero. Neither
the vector nor the flavour non-singlet axial vector currents need
renormalization. Further, there is no mixing between four-fermion operators in
different chiral representations. The order parameter of chiral symmetry
requires, however, a subtraction which is given here explicitly. These results
are based on the fact that the fixed point action satisfies the Ginsparg-Wilson
remnant chiral symmetry condition. On chiral symmetry related questions any
other local solution of this condition will produce similar results.Comment: 10 pages, Late
An Effective Action for Finite Temperature QCD with Fermions
Using lattice perturbation theory at finite temperature, we compute for
staggered fermions the one-loop fermionic corrections to the spatial and
temporal plaquette couplings as well as the leading symmetry breaking
coupling. Numerical and analytical considerations indicate that the finite
temperature corrections to the zero-temperature calculation of A. Hasenfratz
and T. DeGrand are small for small values of , but
become significant for intermediate values of . The effect of these
finite temperature corrections is to ruin the agreement of the
Hasenfratz-DeGrand calculation with Monte Carlo data. We conjecture that the
finite temperature corrections are suppressed nonperturbatively at low
temperatures, resolving this apparent disagreement. The symmetry breaking
coupling is small; we argue that it may change the order of the transition
while having little effect on the critical value of .Comment: 3 pages, 3 figures, latex, self-extracting, Lattice '94 contributio
The absence of cut--off effects for the fixed point action in 1--loop perturbation theory
In order to support the formal renormalization group arguments that the fixed
point action of an asymptotically free model gives cut--off independent
physical predictions in 1--loop perturbation theory, we calculate the finite
volume mass--gap in the non--linear --model. No cut--off effect
of the type is seen for any . The results are
compared with those of the standard and tree level improved Symanzik actions.Comment: 8 pages (latex) + 1 figure (Postscript), uuencode
Asymptotic freedom with discrete spin variables?
We study the critical behaviour of the 2d dodecahedron spin model and
investigate the conjecture that the discrete model describes the same continuum
theory as the O(3) non-linear sigma model. In particular, we found that the
anisotropy of the magnetization A(z) measured in a fixed physical volume
decreases with increasing correlation length, at least up to \xi \approx 1000.Comment: 5 pages, 4 figure
Towards a perfect fixed point action for SU(3) gauge theory
We present an overview of the construction and testing of actions for SU(3)
gauge theory which are approximate fixed points of renormalization group
equations (at ). Such actions are candidates for use
in numerical simulations on coarse lattices.Comment: 6 pages, uuencoded compressed postscript file, contribution to LAT9
First results in QCD with 2+1 light flavors using the fixed-point action
This is a progress report on 2+1 flavor simulation with the FP action on a
lattice with spatial size L=1.2fm. Since m_{ud} is quite small in our
simulation we are in the delta regime for the two light flavors where the low
lying excitations are described by a quantum mechanical rotator. From here we
extract the low energy constant F. We also measure the AWI mass and present
results on numerical issues like low-mode averaging and autocorrelation times.Comment: 7 pages, 6 figures, parallel talk at LATTICE 200
The equivalence of the SU(N) Yang Mills Theory with a Purely Fermionic Model
We investigate the detailed conditions under which a purely fermionic model
with current-current interaction goes over to a renormalizable, asymptotically
free SU gauge theory.Comment: 8 pages, eqs.(6) and (17) are appended as postscipt files at the en
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