Discrepancy in the cross section minimum of elastic nucleon-deuteron scattering

\ensuremath{\Delta}-isobar excitation in the nuclear medium yields an effective three-nucleon force. A coupled-channel formulation of nucleon-deuteron scattering with \ensuremath{\Delta}-isobar excitation developed previously is used. The three-particle scattering equations are solved by a separable expansion of the two-baryon transition matrix below the inelastic threshold of pion production. The effect of \ensuremath{\Delta}-isobar excitation on the spin-averaged differential cross section is studied. The discrepancy between theory and experiment in the diffraction minimum is reduced.