A lattice model of critical dense polymers O(0) is considered for the
finite cylinder geometry. Due to the presence of non-contractible loops with a
fixed fugacity ξ, the model is a generalization of the critical dense
polymers solved by Pearce, Rasmussen and Villani. We found the free energy for
any height N and circumference L of the cylinder. The density ρ of
non-contractible loops is found for N→∞ and large L. The
results are compared with those obtained for the anisotropic quantum chain with
twisted boundary conditions. Using the latter method we obtained ρ for any
O(n) model and an arbitrary fugacity.Comment: arXiv admin note: text overlap with arXiv:0810.223