  We investigate the Mott transitions in two-orbital Hubbard systems. Applying
the dynamical mean field theory and the self-energy functional approach, we
discuss the stability of itinerant quasi-particle states in each band. It is
shown that separate Mott transitions occur at different Coulomb interaction
strengths in general. On the other hand, if some special conditions are
satisfied for the interactions, spin and orbital fluctuations are equally
enhanced at low temperatures, resulting in a single Mott transition. The phase
diagrams are obtained at zero and finite temperatures. We also address the
effect of the hybridization between two orbitals, which induces the Kondo-like
heavy fermion states in the intermediate orbital-selective Mott phase.
