  A substantial fraction of barred galaxies host additional nuclear bars which
tumble with pattern speeds exceeding those of the large-scale (primary) stellar
bars. We have investigated the mechanism of formation and dynamical decoupling
in such nested bars which include gaseous (secondary) nuclear bars within the
full size galactic disks, hosting a double inner Lindblad resonance. Becoming
increasingly massive and self-gravitating, the nuclear bars lose internal
(circulation) angular momentum to the primary bars and increase their strength.
Developing chaos within these bars triggers a rapid gas collapse -- bar
contraction. During this time period, the secondary bar pattern speed
Omega_s~a^{-1}, where "a" stands for the bar size. As a result, Omega_s
increases dramatically until a new equilibrium is reached (if at all), while
the gas specific angular momentum decreases -- demonstrating the dynamical
decoupling of nested bars. Viscosity, and therefore the gas presence, appears
to be a necessary condition for the prograde decoupling of nested bars. This
process maintains an inflow rate of ~1 M_o/yr over ~10^8 yrs across the central
200 pc and has important implications for fueling the nuclear starbursts and
AGN.
