Three-nucleon system: Irreducible and reducible contributions of the three-nucleon force

TL;DR

This paper investigates the effects of irreducible and reducible three-nucleon forces on bound states and scattering observables by solving coupled-channel equations including $ riangle$ isobar excitations.

Contribution

It introduces a coupled-channel approach incorporating $ riangle$ isobar excitations to analyze three-nucleon forces and their impact on nuclear observables.

Findings

Three-nucleon force effects influence bound-state energies.

Reducible contributions significantly affect scattering observables.

Coulomb interaction effects are included via screening and renormalization.

Abstract

The three-nucleon bound and scattering equations are solved in momentum space for a coupled-channel Hamiltonian. The Hamiltonian couples the purely nucleonic sector of Hilbert space with a sector in which one nucleon is excited to a $\Delta$ isobar. The interaction consists of irreducible two-baryon and irreducible three-baryon potentials. The calculation keeps only the purely nucleonic one among the irreducible three-baryon potentials. The coupled-channel two-baryon potential yields additional reducible contributions to the three-nucleon force. The Coulomb interaction between the two protons is included using the method of screening and renormalization. Three-nucleon force effects on the bound-state energies and on observables of elastic nucleon-deuteron scattering and breakup are studied.