The role of heavy fermions

Heavy dynamical fermions with masses around the cut-off do not change the low energy physics apart from a finite renormalization of the gauge coupling. In this paper we study how light the heavy fermions have to be to cause more than this trivial renormalization.Comment: uuencoded 3 page postscript contribution to Lattice 93, COLO-HEP-33

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 $Z_N$ 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 $\kappa = {1\over 2m_F}$, but become significant for intermediate values of $\kappa$. 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 $Z_N$ 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 $\beta$.Comment: 3 pages, 3 figures, latex, self-extracting, Lattice '94 contributio

Dynamical Simulations with Smeared Link Staggered Fermions

One of the most serious problems of the staggered fermion lattice action is flavor symmetry violation. Smeared link staggered fermions can improve flavor symmetry by an order of magnitude relative to the standard thin link action. Over the last few years different smearing transformations have been proposed, both with perturbatively and non-perturbatively determined coefficients. What hindered the acceptance and more general use of smeared link fermions until now is the relative difficulty of dynamical simulations and the lack of perturbative calculations with these actions. In both areas there have been significant improvement lately, that I will review in this paper.Comment: 9 pages,5 figures; Plenary talk contribution to Lattice'200

Improving the Partial-Global Stochastic Metropolis Update for Dynamical Smeared Link Fermions

We discuss several methods that improve the partial-global stochastic Metropolis (PGSM) algorithm for smeared link staggered fermions. We present autocorrelation time measurements and argue that this update is feasible even on reasonably large lattices.Comment: 3 pages, 3 figures, Lattice2002(algor

Improved gradient flow for step scaling function and scale setting

The gradient flow renormalized coupling offers a simple and relatively inexpensive way to calculate the step scaling function and the lattice scale, but both applications can be hindered by large lattice artifacts. Recently we introduced an empirical non-perturbative improvement that can reduce, even remove $\mathcal{O}(a^2)$ lattice artifacts. The method is easy to implement and can be applied to any lattice gauge theory of interest both in step scaling studies and for scale setting. In this talk I will briefly review this improvement method and discuss its application for determining the discrete $\beta$ function of the 8 and 12 flavor SU(3) systems and for improved scale setting in 2+1+1 flavor QCDComment: 7 pages; Contribution to The 32nd International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia University New York, N

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 $SU(3)$ 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 $G = L \sqrt{\sigma(L)}$ where the string tension $\sigma(L)$ is measured from the torelon mass $\mu = L \sigma(L)$. We measure $G$ on lattices of fixed physical volume and varying lattice spacing $a$ (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 $1/2 \ge aT_c \ge 1/6$. Similar behaviour is found for the potential measured in a fixed physical volume.Comment: 28 pages (latex) + 11 figures (Postscript), uuencode

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 $m_q^c$ 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