Comments on "Angular Momentum Transport in Quasi-Keplerian Accretion Disks"

Subramanian, Pujari and Becker (2004) claim that the correct expression forthe angular momentum transport in an accretion disc, which is proportional todOmega/dR, can be derived on the basis of the analysis of the epicyclic motionof gas parcels in adjacent eddies in the disc. We study their argument and showthat their derivation contains several fundamental errors: 1) the biased choiceof the desired formula from an infinite number of formulae; 2) the biasedchoice of parcel trajectories; and 3) confusion regarding the reference frames.Following 1) we could derive, for example, a (invalid) formula in which theangular momentum transport is proportional to dv_phi/dR, and from 2) we couldeven prove that the angular momentum transport is either inward or null. Wepresent the correct approach to the problem of angular momentum transport in anaccretion disc in terms of mean free path theory.Comment: 9 pages, 2 figures, to appear in Prog. Theor. Phys. Vol.113, No.6, 200