Exact identities among the nth extended s-wave-pairing amplitudes in the Hubbard model are presented. They provide more constraints on the possible symmetries of the superconducting gap in the Hubbard model than that between the on-site and the first extended s-wave pairings pointed out by Zhang. For the t-J model, we also find an exact identity between the on-site and the first extended s-wave-pairing amplitudes, which is essentially consistent with that in the Hubbard model. Besides the s-wave pairings, we discuss the constraints on the other pairing amplitudes.

• Received 23 December 1991

DOI:https://doi.org/10.1103/PhysRevB.45.12502