Effective particle-particle interaction in the two-dimensional Hubbard model

The irreducible particle-particle interaction ${\mathrm{\Gamma }}_{\mathit{I}}$ of the two-dimensional Hubbard model is calculated by quantum Monte Carlo simulations. The Bethe-Salpeter equation for the pair-wave function is then solved using the Monte Carlo data for ${\mathrm{\Gamma }}_{\mathit{I}}$ and the single-particle Green’s function. The dominant pairing correlations in the intermediate-coupling regime and at small dopings are discussed.