  Disk formation in magnetized cloud cores is hindered by magnetic braking.
Previous work has shown that for realistic levels of core magnetization, the
magnetic field suppresses the formation of rotationally supported disks during
the protostellar mass accretion phase of low-mass star formation both in the
ideal MHD limit and in the presence of ambipolar diffusion for typical rates of
cosmic ray ionization. Additional effects, such as ohmic dissipation, the Hall
effect, and protostellar outflow, are needed to weaken the magnetic braking and
enable the formation of persistent, rotationally supported, protostellar disks.
In this paper, we first demonstrate that the classic microscopic resistivity is
not large enough to enable disk formation by itself. We then experiment with a
set of enhanced values for the resistivity in the range
$\eta=10^{17}$--$10^{22}$ cm^2/s. We find that a value of order $10^{19}$
cm^2/s is needed to enable the formation of a 100 AU-scale Keplerian disk; the
value depends somewhat on the degree of core magnetization. The required
resistivity is a few orders of magnitude larger than the classic microscopic
values. Whether it can be achieved naturally during protostellar collapse
remains to be determined.
