Disc formation in turbulent cloud cores: is magnetic flux loss necessary
  to stop the magnetic braking catastrophe or not?
  Recent numerical analysis of Keplerian disk formation in turbulent,
magnetized cloud cores by Santos-Lima, de Gouveia Dal Pino, & Lazarian (2012)
demonstrated that reconnection diffusion is an efficient process to remove the
magnetic flux excess during the build up of a rotationally supported disk. This
process is induced by fast reconnection of the magnetic fields in a turbulent
flow. In a similar numerical study, Seifried et al. (2012) concluded that
reconnection diffusion or any other non-ideal MHD effects would not be
necessary and turbulence shear alone would provide a natural way to build up a
rotating disk without requiring magnetic flux loss. Their conclusion was based
on the fact that the mean mass-to-flux ratio ({\mu}) evaluated over a spherical
region with a radius much larger than the disk is nearly constant in their
models. In this letter we compare the two sets of simulations and show that
this averaging over large scales can mask significant real increases of {\mu}
in the inner regions where the disk is built up. We demonstrate that
turbulence-induced reconnection diffusion of the magnetic field happens in the
initial stages of the disk formation in the turbulent envelope material that is
accreting. Our analysis is suggestive that reconnection diffusion is present in
both sets of simulations and provides a simple solution for the "magnetic
braking catastrophe" which is discussed in the literature in relation to the
formation of protostellar accretion disks.
