Universality class of interacting directed single- and double-strand homopolymers.

This work examines a field theory for directed homopolymers in a good solvent. The field theory is based on a lattice model for single- and double-strand polymers with length variables, direction-dependent pairing energy and interactions. As for the less explicit O(n)-symmetric model, there is a close relation to the conventional one-component branched polymer and the associated Lee-Yang problem. We derive results in the limiting cases of nearly complete denaturation and nearly complete renaturation. The single-strand critical exponent is calculated in two-loop order. A plausible physical realization is RNA molecules with a periodic base sequence like AUAU.