  We study the one-dimensional two-orbital Hubbard model with general local
interactions including a pair-hopping term. The model might be realized in
one-dimensional transition-metal nanowires. Phase diagrams at T=0 are obtained
by numerical integration of renormalization group equations and bosonization.
Particular attention is paid to the effects of orbital degeneracy (or
near-degeneracy), interactions favoring locally high-spin configurations, and
velocity differences. Dynamical symmetry enlargement and duality approaches are
employed to determine ground states and to understand quantum phase transitions
between them. An important result is that the pair-hopping term and associated
orbital symmetry can lead to new insulating states. The ground state for
spin-polarized case is also discussed.
