Variational wave functions with Δ-isobar components are used to study trinucleon magnetic moments, the Gamow-Teller matrix element of tritium β decay, thermal neutron radiative capture on , and low-energy proton weak capture on . The Δ-isobar components are generated by transition correlation operators acting on realistic nuclear wave functions. These correlations are obtained from a fit to exact two-body ground-state and low-energy scattering solutions for the Argonne and interaction models, which include Δ-isobar degrees of freedom. Contributions of Δ isobars to electroweak current operators appear at the one-body level in this formalism. Their effect on low-energy electroweak transitions is significantly smaller than that obtained in perturbation theory analyses, where Δ-isobar effects are commonly subsumed into effective two-body current operators. The resulting theoretical cross section for thermal neutron radiative capture on is ≊86 μb, compared to an experimental value of 55±3 μb; the astrophysical S factor for proton weak capture on is predicted to be in the range (1.4–3.2)× MeV b.
- Received 25 November 1991
- Published in the issue dated June 1992
© 1992 The American Physical Society