  We investigate the formation and evolution of circumstellar disks in
turbulent cloud cores until several 104 years after protostar formation using
smoothed particle hydrodynamics (SPH) calculations. The formation and evolution
process of circumstellar disk in turbulent cloud cores differs substantially
from that in rigidly rotating cloud cores. In turbulent cloud cores, a
filamentary structure appears before the protostar formation and the protostar
forms in the filament. If the turbulence is initially sufficiently strong, the
remaining filament twists around the protostar and directly becomes a
rotation-supported disk. Upon formation, the disk orientation is generally
misaligned with the angular momentum of its host cloud core and it dynamically
varies during the main accretion phase, even though the turbulence is weak.
This is because the angular momentum of the entire cloud core is mainly
determined by the large scale velocity field whose wavelength is comparable to
the cloud scale, whereas the angular momentum of the disk is determined by the
local velocity field where the protostar forms and these two velocity fields do
not correlate with each other. In the case of disk evolution in a binary or
multiple stars, the disks are misaligned with each other at least during the
main accretion phase, because there is no correlation between the velocity
fields around the position where each protostar forms. In addition, each disk
is also misaligned with the binary orbital plane. Such misalignment can explain
the recent observations of misaligned disks and misaligned protostellar
outflows.
