⌬-isobar excitation in the nuclear medium yields an effective three-nucleon force. A coupled-channel formulation of nucleon-deuteron scattering with ⌬-isobar excitation developed previously is used. The threeparticle scattering equations are solved by a separable expansion of the two-baryon transition matrix below the inelastic threshold of pion production. The effect of ⌬-isobar excitation on the spin-averaged differential cross section is studied. The discrepancy between theory and experiment in the diffraction minimum is reduced. ͓S0556-2813͑98͒06510-8͔

Breakup in nucleon-deuteron scattering is described. The description is based on a coupled-channel twobaryon potential that allows for the virtual excitation of a nucleon to a ⌬ isobar. The Coulomb interaction is not included. Channel coupling gives rise to an effective three-nucleon force. The three-particle scattering equations are solved by real-axis integration using a separable expansion of the two-baryon transition matrix. Examples for spin-averaged and spin-dependent observables are calculated and compared with experimental data.

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