  We study the formation and early evolution of young stellar objects (YSOs)
using three-dimensional non-ideal magnetohydrodynamic (MHD) simulations to
investigate the effect of cosmic ray ionization rate and dust fraction (or
amount of dust grains) on circumstellar disk formation. Our simulations show
that a higher cosmic ray ionization rate and a lower dust fraction lead to (i)
a smaller magnetic resistivity of ambipolar diffusion, (ii) a smaller disk size
and mass, and (iii) an earlier timing of outflow formation and a greater
angular momentum of the outflow. In particular, at a high cosmic ray ionization
rate, the disks formed early in the simulation are dispersed by magnetic
braking on a time scale of about 104 years. Our results suggest that the cosmic
ray ionization rate has a particularly large impact on the formation and
evolution of disks, while the impact of the dust fraction is not significant.
