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The effective potential of Yang-Mills theory at high temperature derived by Gross, Pisarski, Yaffe and Weiss is critically reexamined and it is argued that the groundstate of the potential at =0 is invalid, due to the infrared divergence of the Matsubara zero mode. This suggests that the thermal groundstate is dominated by infrared non-perturbative effects. Lattice simulations are carried out and the field A0 in the static gauge is observed to acquire nonzero, non-perturbative expectation values at high temperatures. A consequence is that thermal perturbation theory is inconsistent with the non-perturbative groundstate and it cannot account for all of the contributions to a thermodynamic quantity at any temperature. Related issues, including dimensional reduction and confinement, are also discussed., Comment: 31-page main text with 7 figures plus supplements

The low energy effective theory of N=4 super-Yang-Mills theory on S^3 with an R-symmetry chemical potential is shown to be the lowest Landau level system. This theory is a holomorphic complex matrix quantum mechanics. When the value of the chemical potential is not far below the mass of the scalars, the states of the effective theory consist only of the half-BPS states. The theory is solved by the operator method and by utilizing the lowest Landau level projection prescription for the value of the chemical potential less than or equal to the mass of the scalars. When the chemical potential is below the mass, we find that the degeneracy of the lowest Landau level is lifted and the energies of the states are computed. The one-loop correction to the effective potential is computed for the commuting fields and treated as a perturbation to the tree level quantum mechanics. We find that the perturbation term has non-vanishing matrix elements that mix the states with the same R-charge., Comment: 30 pages, 3 figures; in section 2, more explanations added and typos corrected

We address two questions related to the procedure of identifying center vortices based on center projection in maximal center gauge: 1. How does the procedure work, why is it expected to locate center vortices relevant for confinement, and why does it in some cases fail, on lattice configurations preconditioned in a special way? 2. Does the mechanism work the same way for 3 colors instead of 2? (The paper is an abridged version of two recent e-prints, hep-lat/9910033 and hep-lat/9911006.), Comment: Invited talk presented by S. Olejnik at the NATO Advanced Research Workshop ``Lattice Fermions and Structure of the Vacuum'', October 5-9, 1999, Dubna (Russia). 8 pages, 4 EPS figures, LaTeX, uses crckapb.sty, epsf.sty, subfigure.sty, and times.sty

We argue that the ``vortex-finding'' property of maximal center gauge, i.e. the ability of this gauge to locate center vortices inserted by hand on any given lattice, is the key to its success in extracting the vortex content of thermalized lattice configurations. We explain how this property comes about, and why it is expected not only in maximal center gauge, but also in an infinite class of gauge conditions based on adjoint-representation link variables. In principle, the vortex-finding property can be foiled by Gribov copies. This fact is relevant to a gauge-fixing procedure devised by Kovacs and Tomboulis, where we show that the loss of center dominance, found in their procedure, is explained by a corresponding loss of the vortex-finding property. The association of center dominance with the vortex-finding property is demonstrated numerically in a number of other gauges., Comment: 21 pages, 10 figures, Latex2e

We present several new results which pertain to the successes of center projection in maximal center gauge (MCG). In particular, we show why any center vortex, inserted "by hand" into a thermalized lattice configuration, will be among the set of vortices found by the center projection procedure. We show that this "vortex-finding property" is lost when gauge-field configurations are fixed to Landau gauge prior to the maximal center gauge fixing; this fact accounts for the loss of center dominance in the corresponding projected configurations. Variants of maximal center (adjoint Landau) gauge are proposed which correctly identify relevant center vortices., Comment: LATTICE99(confine), 3 pages, 3 figures