Twisted space-time reduced model of large N QCD with two adjoint Wilson fermions

The space-time reduced model of large N QCD with two adjoint Wilson fermions is constructed by applying the symmetric twist boundary conditions with nonvanishing flux k. For large but finite N = L-2, the model should behave as the large N version of the ordinary lattice gauge model on a V = L-4 space-time volume. We perform a comparison of the N dependence of several quantities in this model and in the k = 0 model (corresponding to periodic boundary conditions). Although the Z(4)(N) symmetry seems unbroken in all cases, the N-dependence analysis favors the use of the same values of k and L for which the symmetry is also unbroken in the pure gauge case. In particular, the k = 0 model, studied recently by several authors, shows a large and irregular dependence on N within our region of parameters. This makes this reduced model very impractical for extracting physical information about the large N lattice theory. On the contrary, the model for N = 289 = 17(2) and large enough k gives consistent results, even for extended observables as Wilson loops W(R, T) up to R, T = 8, matching the expected behavior for the lattice model with a 174 space-time volume.