  We investigate the dependence of the ground state of a multi-level quantum
dot on the coupling to an external fermionic system and on the interactions in
the dot. As the coupling to the external system increases, the rearrangement of
the effective energy levels in the dot signals the transition from the Kondo
regime to a mixed valence (MV) regime. The MV regime in a two level dot is
characterized by an intrinsic mixing of the levels in the dot, resulting in
non-perturbative sub- and super-tunneling phenomena that strongly influence the
Kondo effect.
