at h = 0 and k = 0, and the value of D(k, h) at this point depends on the order of limits. We also present numerical evaluations of the free energy W (k, h) and the gluon propagator D(k, h) for the case of SU(2) Yang-Mills theory in various dimensions which support all of these findings.PACS numbers: 11.10. Kk; 11.15.Ha; 12.38.Aw; 14.70.Dj * Supported by the DFG under grant number MA 3935/5-1; axelmaas@web.de † dz2@nyu.edu 2
I. INTRODUCTIONThe free energy, and its Legendre transform, the quantum effective action, play a central role in quantum field theories. As the generating functionals of correlation functions, their knowledge, in principle, grants access to all there is to know about a theory. It is often assured that these functionals are analytic in their external sources, at least away from phase transitions, and thus their derivatives yield, in a well-defined manner, the correlation functions.However, recently this assumption yielded colliding results: Assuming this analyticity, the minimal Landau gauge gluon propagator has necessarily to vanish at zero (Euclidean) momentum [1,2]. At the same time, lattice calculations, which do not need external sources, found this propagator to be finite, at least in three and four dimensions 1 [3-8] for a review.At the same time, continuum calculations using functional methods, where the functional equations were derived under this assumption, found both solutions [14][15][16][17][18]. See [9] for a review of the situation.The logical starting point to resolve this discrepancy is therefore to check the analyticity of the free energy. This is the aim in this work.To this end, we shall be concerned with the Euclidean correlators of gluons in QCD with an arbitrary gauge group, here chosen to be SU(N), for the local gauge symmetry that are fixed to the minimal Landau gauge. These are the fundamental quantities in quantum field theory.The minimal Landau gauge [9] is obtained by minimizing the Hilbert square normto some local minimum (in general not an absolute minimum) with respect to local gauge transformations g(x). These act according tog A|| 2 is stationary and its second variation is positive. It is well known that these two properties imply respectively that the Landau gauge (transversality) condition is satisfied, ∂ · A = 0, and that the Faddeev-Popov operator is positive i. e.(ω, M(A)ω) ≥ 0 for all ω. Here the Faddeev-Popov operator acts according to [9] that in general there are more than one local minimum of F A (g), and we do not specify which local minimum is achieved. This gauge is realized numerically by minimizing a lattice analog of F A (g) by some algorithm, and the local minimum achieved is in general algorithm dependent. However, for all commonly employed algorithms this does not yield different expectation values, as they all are equivalent to an averaging over the first Gribov region [9,20].The analytic bounds which we shall obtain in section II follow from the restriction of the gauge-fixed configurations to the Gribov region Ω, and are the same wheth...