Constraints from Dust Mass and Mass Accretion Rate Measurements on
  Angular Momentum Transport in Protoplanetary Disks
  We investigate the relation between disk mass and mass accretion rate to
constrain the mechanism of angular momentum transport in protoplanetary disks.
Dust mass and mass accretion rate in Chamaeleon I are correlated with a slope
close to linear, similar to the one recently identified in Lupus. We
investigate the effect of stellar mass and find that the intrinsic scatter
around the best-fit Mdust-Mstar and Macc-Mstar relations is uncorrelated. Disks
with a constant alpha viscosity can fit the observed relations between dust
mass, mass accretion rate, and stellar mass, but over-predict the strength of
the correlation between disk mass and mass accretion rate when using standard
initial conditions. We find two possible solutions. 1) The observed scatter in
Mdust and Macc is not primoridal, but arises from additional physical processes
or uncertainties in estimating the disk gas mass. Most likely grain growth and
radial drift affect the observable dust mass, while variability on large time
scales affects the mass accretion rates. 2) The observed scatter is primordial,
but disks have not evolved substantially at the age of Lupus and Chamaeleon I
due to a low viscosity or a large initial disk radius. More accurate estimates
of the disk mass and gas disk sizes in a large sample of protoplanetary disks,
either through direct observations of the gas or spatially resolved
multi-wavelength observations of the dust with ALMA, are needed to discriminate
between both scenarios or to constrain alternative angular momentum transport
mechanisms such as MHD disk winds.
