15 research outputs found
A New Precision Measurement of the 3He(4He,gamma)7Be Cross section
The 3He(4He,gamma)7Be reaction plays an important role in determining the
high energy solar neutrino flux and in understanding the abundances of
primordial 7Li. The present paper reports a new precision measurement of the
cross sections of this direct capture reaction, determined by measuring the
ensuing 7Be activity in the region of Ec.m.=400 keV to 950 keV. Various recent
theoretical fits to our data result in a consistent extrapolated value of
S34(0)=0.53(2)(1).Comment: 10 pages 3 figure
Alpha scattering and capture reactions in the A = 7 system at low energies
Differential cross sections for He- scattering were measured in
the energy range up to 3 MeV. These data together with other available
experimental results for He and H scattering were
analyzed in the framework of the optical model using double-folded potentials.
The optical potentials obtained were used to calculate the astrophysical
S-factors of the capture reactions HeBe and
HLi, and the branching ratios for the transitions into
the two final Be and Li bound states, respectively. For
HeBe excellent agreement between calculated and
experimental data is obtained. For HLi a value
has been found which is a factor of about 1.5 larger than the adopted value.
For both capture reactions a similar branching ratio of has been obtained.Comment: submitted to Phys.Rev.C, 34 pages, figures available from one of the
authors, LaTeX with RevTeX, IK-TUW-Preprint 930540
Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields
We analyze in details the standard Primordial Nucleosynthesis scenario. In
particular we discuss the key theoretical issues which are involved in a
detailed prediction of light nuclide abundances, as the weak reaction rates,
neutrino decoupling and nuclear rate modeling. We also perform a new analysis
of available data on the main nuclear processes entering the nucleosynthesis
reaction network, with particular stress on their uncertainties as well as on
their role in determining the corresponding uncertainties on light nuclide
theoretical estimates. The current status of theoretical versus experimental
results for 2H, 3He, 4He and 7Li is then discussed using the determination of
the baryon density as obtained from Cosmic Microwave Background anisotropies.Comment: LaTeX, 83 pages, 30 .pdf figures. Some typos in the units of
R-functions in appendix D and relative plots fixe
Modern theories of low-energy astrophysical reactions
We summarize recent ab initio studies of low-energy electroweak reactions of
astrophysical interest, relevant for both big bang nucleosynthesis and solar
neutrino production. The calculational methods include direct integration for
np radiative and pp weak capture, correlated hyperspherical harmonics for
reactions of A=3,4 nuclei, and variational Monte Carlo for A=6,7 nuclei.
Realistic nucleon-nucleon and three-nucleon interactions and consistent current
operators are used as input.Comment: 29 pages, 4 figure
Determination of the 3He+alpha\to 7Be asymp. normalization coefficients (nucl. vertex constants) and their application for extrapolation of the 3He(alpha,gamma)7Be astroph. S-factors to the solar energy region
A new analysis of the modern precise measured astrophysical factors for
the direct capture reaction [B.S. Nara Singh
{\it et al.}, Phys.Rev.Lett. {\bf 93}, 262503 (2004); D. Bemmerer {\it et al.},
Phys.Rev.Lett. {\bf 97}, 122502 (2006); F.Confortola {\it et al.}, Phys.Rev.C
{\bf 75}, 065803 (2007), T.A.D.Brown {\it et al.}, Phys.Rev. C {\bf 76}, 055801
(2007) and A Di Leva, {\it et al.},Phys.Rev.Lett. {\bf 102}, 232502 (2009)]
populating to the ground and first excited states of is carried
out based on the modified two - body potential approach. New estimates are
obtained for the ^{\glqq}indirectly determined\grqq\, values of the
asymptotic normalization constants (the nuclear vertex constants) for (g.s.) and (0.429 MeV) as well as the astrophysical factors at
E 90 keV, including =0. The values of asymptotic normalization
constants have been used for getting information about the -particle
spectroscopic factors for the mirror ()-pair.Comment: 24 pages, 5 figures, 2 table
Updated Nucleosynthesis Constraints on Unstable Relic Particles
We revisit the upper limits on the abundance of unstable massive relic
particles provided by the success of Big-Bang Nucleosynthesis calculations. We
use the cosmic microwave background data to constrain the baryon-to-photon
ratio, and incorporate an extensively updated compilation of cross sections
into a new calculation of the network of reactions induced by electromagnetic
showers that create and destroy the light elements deuterium, he3, he4, li6 and
li7. We derive analytic approximations that complement and check the full
numerical calculations. Considerations of the abundances of he4 and li6 exclude
exceptional regions of parameter space that would otherwise have been permitted
by deuterium alone. We illustrate our results by applying them to massive
gravitinos. If they weigh ~100 GeV, their primordial abundance should have been
below about 10^{-13} of the total entropy. This would imply an upper limit on
the reheating temperature of a few times 10^7 GeV, which could be a potential
difficulty for some models of inflation. We discuss possible ways of evading
this problem.Comment: 40 pages LaTeX, 18 eps figure
Primordial Nucleosynthesis for the New Cosmology: Determining Uncertainties and Examining Concordance
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) have
a long history together in the standard cosmology. The general concordance
between the predicted and observed light element abundances provides a direct
probe of the universal baryon density. Recent CMB anisotropy measurements,
particularly the observations performed by the WMAP satellite, examine this
concordance by independently measuring the cosmic baryon density. Key to this
test of concordance is a quantitative understanding of the uncertainties in the
BBN light element abundance predictions. These uncertainties are dominated by
systematic errors in nuclear cross sections. We critically analyze the cross
section data, producing representations that describe this data and its
uncertainties, taking into account the correlations among data, and explicitly
treating the systematic errors between data sets. Using these updated nuclear
inputs, we compute the new BBN abundance predictions, and quantitatively
examine their concordance with observations. Depending on what deuterium
observations are adopted, one gets the following constraints on the baryon
density: OmegaBh^2=0.0229\pm0.0013 or OmegaBh^2 = 0.0216^{+0.0020}_{-0.0021} at
68% confidence, fixing N_{\nu,eff}=3.0. Concerns over systematics in helium and
lithium observations limit the confidence constraints based on this data
provide. With new nuclear cross section data, light element abundance
observations and the ever increasing resolution of the CMB anisotropy, tighter
constraints can be placed on nuclear and particle astrophysics. ABRIDGEDComment: 54 pages, 20 figures, 5 tables v2: reflects PRD version minor changes
to text and reference