1,156 research outputs found
Weak proton capture on 3He
The astrophysical S-factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to realistic Hamiltonians consisting of the Argonne v14 or
Argonne v18 two-nucleon and Urbana-VIII or Urbana-IX three-nucleon
interactions. The nuclear weak charge and current operators have vector and
axial-vector components, that include one- and many-body terms. All possible
multipole transitions connecting any of the p 3He S- and P-wave channels to the
4He bound state are considered. The S-factor at a p 3He center-of-mass energy
of 10 keV, close to the Gamow-peak energy, is predicted to be 10.1 10^{-20} keV
b with the AV18/UIX Hamiltonian, a factor of about 4.5 larger than the value
adopted in the standard solar model. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor. The energy
dependence is rather weak: the AV18/UIX zero-energy S-factor is 9.64 10^{-20}
keV b, only 5 % smaller than the 10 keV result quoted above. The model
dependence is also found to be weak: the zero-energy S-factor is calculated to
be 10.2 10^{-20} keV b with the older AV14/UVIII model, only 6 % larger than
the AV18/UIX result. Our best estimate for the S-factor at 10 keV is therefore
(10.1 \pm 0.6) 10^{-20} keV b, when the theoretical uncertainty due to the
model dependence is included. This value for the calculated S-factor is not as
large as determined in fits to the Super-Kamiokande data in which the hep flux
normalization is free. However, the precise calculation of the S-factor and the
consequent absolute prediction for the hep neutrino flux will allow much
greater discrimination among proposed solar neutrino oscillation solutions.Comment: 54 pages RevTex file, 6 PostScript figures, submitted to Phys. Rev.
Realistic Calculation of the hep Astrophysical Factor
The astrophysical factor for the proton weak capture on 3He is calculated
with correlated-hyperspherical-harmonics bound and continuum wave functions
corresponding to a realistic Hamiltonian consisting of the Argonne v18
two-nucleon and Urbana-IX three-nucleon interactions. The nuclear weak charge
and current operators have vector and axial-vector components, that include
one- and many-body terms. All possible multipole transitions connecting any of
the p-3He S- and P-wave channels to the 4He bound state are considered. The
S-factor at a p-3He center-of-mass energy of 10 keV, close to the Gamow-peak
energy, is predicted to be 10.1 10^{-20} keV b, a factor of five larger than
the standard-solar-model value. The P-wave transitions are found to be
important, contributing about 40 % of the calculated S-factor.Comment: 8 pages RevTex file, submitted to Phys. Rev. Let
Muon capture on deuteron and 3He
The muon capture reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are
studied with conventional or chiral realistic potentials and consistent weak
currents. The initial and final A=2 and 3 nuclear wave functions are obtained
from the Argonne v18 or chiral N3LO two-nucleon potential, in combination with,
respectively, the Urbana IX or chiral N2LO three-nucleon potential in the case
of A=3. The weak current consists of polar- and axial-vector components. The
former are related to the isovector piece of the electromagnetic current via
the conserved-vector-current hypothesis. These and the axial currents are
derived either in a meson-exchange or in a chiral effective field theory
(chiEFT) framework. There is one parameter (either the N-to-\Delta axial
coupling constant in the meson-exchange model, or the strength of a contact
term in the chiEFT model) which is fixed by reproducing the Gamow-Teller matrix
element in tritium beta-decay. The model dependence relative to the adopted
interactions and currents (and cutoff sensitivity in the chiEFT currents) is
weak, resulting in total rates of 392.0 +/- 2.3 Hz for A=2, and 1484 +/- 13 Hz
for A=3, where the spread accounts for this model dependence.Comment: 15 pages, 1 figure, submitted to Phys. Rev.
Polarization observables in p-d scattering below 30 MeV
Differential and total breakup cross sections as well as vector and tensor
analyzing powers for p-d scattering are studied for energies above the deuteron
breakup threshold up to E(lab)=28 MeV. The p-d scattering wave function is
expanded in terms of the correlated hyperspherical harmonic basis and the
elastic S-matrix is obtained using the Kohn variational principle in its
complex form. The effects of the Coulomb interaction, which are expected to be
important in this energy range, have been rigorously taken into account. The
Argonne AV18 interaction and the Urbana URIX three-nucleon potential have been
used to perform a comparison to the available experimental data.Comment: 31 pages, 8 figure
The Ay Problem for p-3He Elastic Scattering
We present evidence that numerically accurate quantum calculations employing
modern internucleon forces do not reproduce the proton analyzing power, A_y,
for p-3He elastic scattering at low energies. These calculations underpredict
new measured analyzing powers by approximately 30% at E_{c.m.} = 1.20 MeV and
by 40% at E_{c.m.} = 1.69 MeV, an effect analogous to a well-known problem in
p-d and n-d scattering. The calculations are performed using the complex Kohn
variational principle and the (correlated) Hyperspherical Harmonics technique
with full treatment of the Coulomb force. The inclusion of the three-nucleon
interaction does not improve the agreement with the experimental data.Comment: Latex file, 4 pages, 2 figures, to be published on Phys. Rev. Let
Variational Calculation on A=3 and 4 Nuclei with Non-Local Potentials
The application of the hyperspherical harmonic approach to the case of
non-local two-body potentials is described. Given the properties of the
hyperspherical harmonic functions, there are no difficulties in considering the
approach in both coordinate and momentum space. The binding energies and other
ground state properties of A=3 and 4 nuclei are calculated using the CD Bonn
2000 and N3LO two-body potentials. The results are shown to be in excellent
agreement with corresponding ones obtained by other accurate techniques.Comment: 12 pages, 6 tables, RevTex
The importance of few-nucleon physics at low energy
This manuscript originated from the discussion at the workshop on the "Future
of Few-body Low Energy Experimental Physics" (FFLEEP), which was held at the
University of Trento on December 4-7, 2002 and has been written in its present
form on March 19, 2003. It illustrates a selection of theoretical advancements
in the nuclear few-body problem, including two- and many-nucleon interactions,
the three-nucleon bound and scattering system, the four-body problem, the
A-body (A4) problem, and fields of related interest, such as reactions of
astrophysical interest and few-neutron systems. Particular attention is called
to the contradictory situation one experiences in this field: while theory is
currently advancing and has the potential to inspire new experiments, the
experimental activity is nevertheless rapidly phasing out. If such a trend will
continue, advancements in this area will become critically difficult.Comment: 29 pages, 21 figures. Manuscript originated from the discussion at
the workshop on the "Future of Few-body Low Energy Experimental Physics"
(FFLEEP), University of Trento, December 4-7, 2002, written in its present
form on March 19, 2003, circulated mainly among the participants to the
FFLEEP workshop. Since the authors have been repeatedly solicited to make the
manuscript accessible to a larger audience potentially interested in its
scientific content, they have decided to post it on this archiv
Calculation of the Alpha--Particle Ground State within the Hyperspherical Harmonic Basis
The problem of calculating the four--nucleon bound state properties for the
case of realistic two- and three-body nuclear potentials is studied using the
hyperspherical harmonic (HH) approach. A careful analysis of the convergence of
different classes of HH functions has been performed. A restricted basis is
chosen to allow for accurate estimates of the binding energy and other
properties of the 4He ground state. Results for various modern two-nucleon and
two- plus three-nucleon interactions are presented. The 4He asymptotic
normalization constants for separation in 2+2 and 1+3 clusters are also
computed.Comment: 29 pages, 4 figures, 11 tables, revtex
The Hyperspherical Harmonics Method: A Tool for Testing and Improving Nuclear Interaction Models
none6siThe Hyperspherical Harmonics (HH) method is one of the most accurate techniques to solve the quantum mechanical problem for nuclear systems with a number of nucleons A ≤ 4. In particular, by applying the Rayleigh-Ritz or Kohn variational principle, both bound and scattering states can be addressed, using either local or non-local interactions. Thanks to this versatility, the method can be used to test the two- and three-nucleon components of the nuclear interaction. In the present review we introduce the formalism of the HH method, both for bound and scattering states. In particular, we describe the implementation of the method to study the A = 3 and 4 scattering problems. Second, we present a selected choice of results of the last decade, most representative of the latest achievements. Finally, we conclude with a discussion of what we believe will be the most significant developments within the HH method for the next 5–10 years.openMarcucci L.E.; Dohet-Eraly J.; Girlanda L.; Gnech A.; Kievsky A.; Viviani M.Marcucci, L. E.; Dohet-Eraly, J.; Girlanda, L.; Gnech, A.; Kievsky, A.; Viviani, M
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