Free energy of a semiflexible polymer in a tube and statistics of a randomly-accelerated particle

The confinement free energy per unit length of a continuous semiflexible polymer or wormlike chain in a tube with a rectangular cross section is derived in the regime P >> L(1), L(2) of strong confinement. Here P is the persistence length, and L(1) and L(2) are the sides of the rectangle. The result is also interpreted in terms of the escape probability of a randomly-accelerated particle from a rectangular domain.