  We demonstrate that growth of stellar bars in spinning dark matter halos is
heavily suppressed in the secular phase of evolution, using numerical
simulations of isolated galaxies. In a representative set of models, we show
that for values of the cosmological spin parameter lambda > 0.03, bar growth
(in strength and size) becomes increasingly quenched. Furthermore, slowdown of
bar pattern speed weakens substantially with increasing `lambda,' until it
ceases completely. The terminal structure of bars is affected as well,
including extent and shape of their boxy/peanut bulges. The essence of this
effect lies in the modified angular momentum exchange between the disk and the
halo facilitated by the bar. For the first time we have demonstrated that a
dark matter halo can emit and not purely absorb angular momentum. Although the
halo as a whole is not found to emit, the net transfer of angular momentum from
the disk to the halo is significantly reduced or completely eliminated. The
paradigm shift implies that the accepted view that disks serve as sources of
angular momentum and halos serve as sinks, must be revised. Halos with lambda >
0.03 are expected to form a substantial fraction, based on lognormal
distribution of lambda. Dependence of secular bar evolution on halo spin,
therefore, implies profound corollaries for the cosmological evolution of
galactic disks.
