Zero-temperature properties of RNA secondary structures

We analyze different microscopic RNA models at zero temperature. We discuss both the most simple model, which suffers a large degeneracy of the ground state, and models in which the degeneracy has been removed in a more or less severe manner. We calculate low-energy density of states using a coupling perturbing method, where the ground state of a modified Hamiltonian, that repels the original ground state, is determined. We evaluate scaling exponents starting from measurements of overlaps and energy differences. In the case of models without accidental degeneracy of the ground state we are able to clearly establish the existence of a glassy phase with $\theta \simeq 1/3.$ 87.15.Aa, 64.60.Fr