Papers Published
Abstract:
The stochastic 2D Navier-Stokes equations on
the torus driven by degenerate noise are
studied. We characterize the smallest closed
invariant subspace for this model and show
that the dynamics restricted to that subspace
is ergodic. In particular, our results yield
a purely geometric characterization of a
class of noises for which the equation is
ergodic in L^2 of the torus. Unlike in
previous works, this class is independent of
the viscosity and the strength of the noise.
The two main tools of our analysis are the
asymptotic strong Feller property, introduced
in this work, and an approximate integration
by parts formula. The first, when combined
with a weak type of irreducibility, is shown
to ensure that the dynamics is ergodic. The
second is used to show that the first holds
under a Hormander-type condition. This
requires some interesting non-adapted
stochastic analysis.