Electro-weak Reactions for Astrophysics

The status of "ab initio" microscopic calculations of the 2H(p,gamma)3He and 3He(p,e+nu_e)4He reactions is reviewed. The methods used to generate accurate nuclear ground- and scattering-state wave functions, and to construct realistic electro-weak transition operators are described. The uncertainties in the theoretical predictions, particularly those relevant to the p-3He weak capture, are discussed. For the dp radiative capture, the theoretical results are compared with the TUNL data in the energy range 0--100 keV.Comment: 10 pages, 3 figures, Few-Body XVI plenary talk, Taipei, March 200

Electromagnetic Structure of Few-Nucleon Systems: a Critical Review

Our current understanding of the structure of nuclei with up to A=8, including energy spectra, electromagnetic form factors, and capture reactions, is critically reviewed within the context of a realistic approach to nuclear dynamics based on two- and three-nucleon interactions and associated electromagnetic currents.Comment: 10 pages, 5 figures, proceedings of the XVIIth European Conference on Few-Body Problems in Physics, Evora, Portuga

Interactions, Currents, and the Structure of Few-Nucleon Systems

Our current understanding of the structure of nuclei with up to A=8, including energy spectra, electromagnetic form factors, and weak transitions, is reviewed within the context of a realistic approach to nuclear dynamics based on two- and three- nucleon interactions and associated electro-weak currents. Low-energy radiative and weak capture reactions of astrophysical relevance involving these light systems are also discussed.Comment: 10 pages, 1 figure, proceedings of the International Nuclear Physics Conference "Bologna 2000 - Structure of the Nucleus at the Dawn of the Century

The Coulomb Sum and Proton-Proton Correlations in Few-Body Nuclei

In simple models of the nuclear charge operator, measurements of the Coulomb sum and the charge form factor of a nucleus directly determine the proton-proton correlations. We examine experimental results obtained for few-body nuclei at Bates and Saclay using models of the charge operator that include both one- and two-body terms. Previous analyses using one-body terms only have failed to reproduce experimental results. However, we find that the same operators which have been used to successfully describe the charge form factors also produce substantial agreement with measurements of the Coulomb sum.Comment: 11 pages, Revtex version 3.0 with 3 Postscript figures appended, ANL preprint PHY-7473-TH-9

Inclusive neutrino scattering off deuteron at low energies in chiral effective field theory

Cross sections for inclusive neutrino scattering off deuteron induced by neutral and charge-changing weak currents are calculated from threshold up to 150 MeV energies in a chiral effective field theory including high orders in the power counting. Contributions beyond leading order (LO) in the weak current are found to be small, and increase the cross sections obtained with the LO transition operators by a couple of percent over the whole energy range (0--150) MeV. The cutoff dependence is negligible, and the predicted cross sections are within $\sim 2$\% of, albeit consistently larger than, corresponding predictions obtained in conventional meson-exchange frameworks.Comment: 16 pages, 10 figures, edits made to the text and added two figures, as suggested by Referee. References adde

The proton-proton weak capture in chiral effective field theory

The astrophysical S-factor for proton-proton weak capture is calculated in chiral effective field theory over the center-of-mass relative-energy range 0--100 keV. The chiral two-nucleon potential derived up to next-to-next-to-next-to leading order is augmented by the full electromagnetic interaction including, beyond Coulomb, two-photon and vacuum-polarization corrections. The low-energy constants (LEC's) entering the weak current operators are fixed so as to reproduce the A=3 binding energies and magnetic moments, and the Gamow-Teller matrix element in tritium beta decay. Contributions from S and P partial waves in the incoming two-proton channel are retained. The S-factor at zero energy is found to be S(0)=(4.030 +/- 0.006) x 10^{-23} MeV fm^2, with a P-wave contribution of 0.020 x 10^{-23} MeV fm^2. The theoretical uncertainty is due to the fitting procedure of the LEC's and to the cutoff dependence.Comment: 4 pages, 3 figures; revisited version accepted for publication on Phys. Rev. Lett. A misprint in Table II has been correcte

Muon capture in nuclei: an ab initio approach based on quantum Monte Carlo methods

An ab initio quantum Monte Carlo method is introduced for calculating total rates of muon weak capture in light nuclei with mass number $A \leq 12$. As a first application of the method, we perform a calculation of the rate in $^4$He in a dynamical framework based on realistic two- and three-nucleon interactions and realistic nuclear charge-changing weak currents. The currents include one- and two-body terms induced by $\pi$- and $\rho$-meson exchange, and $N$-to-$\Delta$ excitation, and are constrained to reproduce the empirical value of the Gamow-Teller matrix element in tritium. We investigate the sensitivity of theoretical predictions to current parametrizations of the nucleon axial and induced pseudoscalar form factors as well as to two-body contributions in the weak currents. The large uncertainties in the measured values obtained from bubble-chamber experiments (carried out over 50 years ago) prevent us from drawing any definite conclusions.Comment: 6 pages, 1 figur