The nature of the viscosity operative in hot, two-temperature accretion disks
around AGN has been a long-standing, unsolved problem. It has been previously
suggested that protons, in conjunction with the turbulent magnetic field that
is likely to exist in the accretion disk, might be crucial in providing this
viscosity. Several authors have recently determined diffusion coefficients for
charged particles (cosmic rays) propagating in turbulent magnetic fields by
means of extensive Monte Carlo simulations. We use the diffusion coefficients
for protons determined by these simulations to find the effective mean free
path for protons in hot accretion disks. This in turn yields good estimates of
the viscosity due to energetic protons embedded in the turbulent magnetic field
of a hot, two-temperature accretion disk. We combine this with a simple
two-temperature accretion disk model to determine the Shakura-Sunyaev α
viscosity parameter arising out of this mechanism. We find that protons
diffusing in the turbulent magentic field embedded in a hot accretion d isk
provide a physically reasonable source of viscosity in hot accretion disks
around AGN.Comment: submitted to proceedings of the 29th International Cosmic Ray Conf.,
Aug 3-10 2005, Pun