Dissolved deconfinement:: Phase structure of large N gauge theories with fundamental matter

A class of large N U(N) gauge theories on a compact manifold S-3 X R (with possible inclusion of adjoint matter) is known to show first-order deconfinement transition at the deconfinement temperature. This includes the familiar example of pure YM theory and N = 4 Supersymmetric Yang-Mills theory. Here we study the effect of introduction of N-f fundamental matter fields in the phase diagram of the above mentioned gauge theories at small coupling and in the limit of large N and finite Nf IN. We find some interesting features like the termination of the line of first-order deconfinement phase transition at a critical point as the ratio N-f/N is increased and absence of deconfinement transition thereafter (there is only a smooth crossover). This result may have some implication for QCD, which unlike a pure gauge theory does not show a first-order deconfinement transition and only displays a smooth crossover at the transition temperature.