  During a stellar tidal disruption event (TDE), an accretion disk forms as
stellar debris returns to the disruption site and circularizes. Rather than
being confined within the circularizing radius, the disk can spread to larger
radii to conserve angular momentum. A spreading disk is a source of matter for
re-accretion at rates which can exceed the later stellar fallback rate,
although a disk wind can suppress its contribution to the central black hole
accretion rate. A spreading disk is detectible through a break in the central
accretion rate history, or, at longer wavelengths, by its own emission. We
model the evolution of TDE disk size and accretion rate, by accounting for the
time-dependent fallback rate, for the influence of wind losses in the early,
advective stage, and for the possibility of thermal instability for accretion
rates intermediate between the advection-dominated and gas-pressure dominated
states. The model provides a dynamic basis for modeling TDE light curves. All
or part of a young TDE disk will precess as a solid body due to Lense-Thirring
effect, and precession may manifest itself as quasi-periodic modulation of
light curve. The precession period increases with time. Applying our results to
the jetted TDE candidate Swift J1644+57, whose X-ray light curve shows numerous
quasi-periodic dips, we argue that the data best fit a scenario in which a
main-sequence star was fully disrupted by an intermediate mass black hole on an
orbit significantly inclined from the black hole equator, with the apparent jet
shutoff at t= 500 d corresponding to a disk transition from the advective state
to the gas-pressure dominated state.
