  The multiorbital Hubbard model is expressed in terms of quantum phase
variables (``slave rotors'') conjugate to the local charge, and of auxiliary
fermions, providing an economical representation of the Hilbert space of
strongly correlated systems. When the phase variables are treated in a local
mean-field manner, similar results to the dynamical mean-field theory are
obtained, namely a Brinkman-Rice transition at commensurate fillings together
with a ``preformed'' Mott gap in the single-particle density of states. The
slave- rotor formalism allows to go beyond the local description and take into
account spatial correlations, following an analogy to the superfluid-insulator
transition of bosonic systems. We find that the divergence of the effective
mass at the metal- insulator transition is suppressed by short range magnetic
correlations in finite-dimensional systems. Furthermore, the strict separation
of energy scales between the Fermi- liquid coherence scale and the Mott gap
found in the local picture, holds only approximately in finite dimensions, due
to the existence of low-energy collective modes related to zero-sound.
