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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 themagnetic flux excess during the build up of a rotationally supported disk. Thisprocess is induced by fast reconnection of the magnetic fields in a turbulentflow. In a similar numerical study, Seifried et al. (2012) concluded thatreconnection diffusion or any other non-ideal MHD effects would not benecessary and turbulence shear alone would provide a natural way to build up arotating disk without requiring magnetic flux loss. Their conclusion was basedon the fact that the mean mass-to-flux ratio ({\mu}) evaluated over a sphericalregion with a radius much larger than the disk is nearly constant in theirmodels. In this letter we compare the two sets of simulations and show thatthis averaging over large scales can mask significant real increases of {\mu}in the inner regions where the disk is built up. We demonstrate thatturbulence-induced reconnection diffusion of the magnetic field happens in theinitial stages of the disk formation in the turbulent envelope material that isaccreting. Our analysis is suggestive that reconnection diffusion is present inboth sets of simulations and provides a simple solution for the "magneticbraking catastrophe" which is discussed in the literature in relation to theformation of protostellar accretion disks.

Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?