388 research outputs found
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 \% 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 . As a
first application of the method, we perform a calculation of the rate in 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 - and -meson exchange, and
-to- 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
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