  This work examines a field theory for RNA-like molecules in a good solvent.
The field theory is based on a lattice model for single- and double-strand RNA
with a periodic base sequence, and otherwise contains all known relevant
details (polymer types, polymer lengths and interactions). As for the somewhat
less explicit $O\left(n\right)$-symmetric model there is a close relation to
the conventional one-component branched polymer and the associated Lee-Yang
problem. We further elucidate this relation. We derive exact results in the
limiting cases of nearly complete denaturation and nearly complete
renaturation. The single-strand critical exponent $\nu_{\varphi}$ is calculated
in two-loop order.
