  We introduce an anisotropic mean-field approach for the dynamics of
semiflexible polymers under intermediate tension, the force range where a chain
is partially extended but not in the asymptotic regime of a nearly straight
contour. The theory is designed to exactly reproduce the lowest order
equilibrium averages of a stretched polymer, and treats the full complexity of
the problem: the resulting dynamics include the coupled effects of long-range
hydrodynamic interactions, backbone stiffness, and large-scale polymer contour
fluctuations. Validated by Brownian hydrodynamics simulations and comparison to
optical tweezer measurements on stretched DNA, the theory is highly accurate in
the intermediate tension regime over a broad dynamical range, without the need
for additional dynamic fitting parameters.
