Results on the symmetries of integrable fermionic models on chains

We investigate integrable fermionic models within the scheme of the graded quantum inverse scattering method, and prove that any symmetry imposed on the solution of the Yang-Baxter equation reflects on the constants of motion of the model; generalizations with respect to known results are discussed. This theorem is shown to be very effective when combined with the polynomial R -matrix technique (PRT): we apply both of them to the study of the extended Hubbard models, for which we find all the subcases enjoying several kinds of (super)symmetries. In particular, we derive a geometrical construction expressing any gl(2, 1)-invariant model as a linear combination of EKS and U-supersymmetric models. Further, we use the PRT to obtain 32 integrable so(4)-invariant models. By joint use of the Sutherland's species technique and eta -pairs construction we propose a general method to derive their physical features, and we provide some explicit results. (C) 2001 Elsevier Science B.V. All rights reserved.