title: Evolution of the Surface Density Structure of a Protoplanetary Disk with a Dead Zone authors: Taku Takeuchi (Tokyo Institute of Technology), Satoshi Okuzumi (Nagoya Univeristy), Takayuki Muto (Tokyo Institute of Technology) abstract: We study evolution of the surface density distributions of protoplanetary disks taking into account the effect of turbulent viscosity via magneto-rotational instability. The inner part of a protoplanetary disk is inactive to MHD turbulence because of its low ionization degree. Recent simulations on MHD turbulence have shown that the mass accretion rate in the dead zone is proportional to the net vertical flux of the magnetic fields threading the disk, B_z. Thus, the surface density structure in the dead zone depends on the radial profile of B_z. We show that for a steady accretion state the radial profile of B_z is uniquely determined for a given value of the mass accretion rate. On the other hand, any surface density profile can be a solution for the steady accretion state, meaning that considering only steady solutions cannot determine the density profile of the disk. The time evolutions of both the surface density and the net vertical flux must be considered simultaneously. In this study, we consider the simplest model in which the evolution of B_z is assumed a priori. The disk gas piles up in the dead zone only if B_z is less than a certain required value to maintain the steady state.