  We discover a new type of nonequilibrium phase transition in a model of
chromatin dynamics, which accounts for the coherent motions that have been
observed in experiment. The coherent motion is due to the long-range
cooperation of molecular motors tethered to chromatin. Cooperation occurs if
each motor acts simultaneously on the polymer and the surrounding solvent,
exerting on them equal and opposite forces. This drives the flow of solvent
past the polymer, which in turn affects the orientation of nearby motors and,
if the drive is strong enough, an active polar (``ferromagnetic'') phase of
motors can spontaneously form. Depending on boundary conditions, either
transverse flows, or sustained longitudinal oscillations and waves are
possible. Predicted time and length scales are consistent with experiments. We
now have in hand a coarse-grained description of chromatin dynamics which
reproduces the directed coherent flows of chromatin seen in experiments. This
field-theoretic description can be analytically coupled to other features of
the nuclear environment such as fluctuating or porous boundaries, local
heterogeneities in the distribution of chromatin or its activity, leading to
insights on the effects of activity on the cell nucleus and its contents.
