Mesonic states and vacuum replicas in potential quark models for QCD

In this paper, we study generic nonlocal Nambu-Jona-Lasinio models for four-dimensional QCD in the limit of a large number of colors. We diagonalize, through a Bogoliubov-type transformation, the Hamiltonian of the model completely in terms of the compound operators creating/annihilating mesons--bound states of dressed quarks and antiquarks - and demonstrate a one-to-one correspondence between the Bogoliubov diagonalization condition and the Bethe-Salpeter equation for bound states. We conclude that, in the leading order in N{sub C}, the nontrivial contents of the theory is entirely encoded in the chiral angle - the solution to the mass-gap equation for dressed quarks. As a consequence, we extend the statement of existence of excited solutions to the mass-gap equation, called vacuum replicas, beyond the BCS level and prescribe a new index to the mesonic operators--the label of the vacuum state in which the corresponding meson is created.