Continuum model for polymers with finite thickness

We consider the continuum limit of a recently introduced model for discretized thick polymers, or tubes. We address both analytically and numerically how the polymer thickness influences the decay of tangent-tangent correlations and find how the persistence length scales with the thickness and the torsional rigidity of the tube centreline. At variance with the worm-like chain model, the phase diagram that we obtain for a continuous tube is richer; in particular, for a given polymer thickness there exists a threshold value for the centreline torsional rigidity separating a simple exponential decay of the tangent-tangent correlation from an oscillatory one. (letter to the editor)