Superconductivity in the Hubbard model with strong Coulomb repulsion

We calculated an effective electron interaction in Cooper's channel for the t-J model with the help of the diagram technique for the Hubbard operators. We derived equations which are similar to the superconducting strong-coupling theory equations and investigated the possibility of superconducting pairing due to spin fluctuations in different regions of (t/U, n)-plane corresponding to different magnetic regimes of the system