Semi-flexible polymers with attractive interactions

The delocalization and unbinding transitions of two semi-flexible polymers which experience attractive interactions are studied by a variety of theore tical methods. In two-dimensional systems, one has to distinguish four diff erent universality classes for the interaction potentials. In particular, t he delocalization transitions from a potential well and the unbinding trans itions from such a well in the presence of a hard wall exhibit distinct cri tical behavior governed by different critical exponents. In three-dimension al systems! we predict first-order transitions with a jump in the energy de nsity but with critical or self-similar fluctuations leading to distributio n functions with poser law tails. The predicted critical behavior is confir med numerically by transfer matrix calculations in two dimensions and by Mo nte Carlo simulations in three dimensions. This behavior should be accessib le to experiments on biopolymers such as actin filaments or microtubuli.