221 research outputs found
Updated Big-Bang Nucleosynthesis compared to WMAP results
From the observations of the anisotropies of the Cosmic Microwave Background
(CMB) radiation, the WMAP satellite has provided a determination of the
baryonic density of the Universe, \Omega_b.h^2, with an unprecedented
precision. This imposes a careful reanalysis of the standard Big-Bang
Nucleosynthesis (SBBN) calculations. We have updated our previous calculations
using thermonuclear reaction rates provided by a new analysis of experimental
nuclear data constrained by -matrix theory. Combining these BBN results with
the \Omega_b.h^2 value from WMAP, we deduce the light element (4He, D, 3He and
7Li) primordial abundances and compare them with spectroscopic observations.
There is a very good agreement with deuterium observed in cosmological clouds,
which strengthens the confidence on the estimated baryonic density of the
Universe. However, there is an important discrepancy between the deduced 7Li
abundance and the one observed in halo stars of our Galaxy, supposed, until
now, to represent the primordial abundance of this isotope. The origin of this
discrepancy, observational, nuclear or more fundamental remains to be
clarified. The possible role of the up to now neglected 7Be(d,p)2\alpha and
7Be(d,\alpha)5Li reactions is considered.Comment: Invited contribution to the Origin of Matter and Evolution of the
Galaxies (OMEG03) conference, RIKEN, Japan. Proceedings to appear in World
Scientifi
Comprehensive two-dimensional gas chromatography (GC x GC) measurements of volatile organic compounds in the atmosphere
Abstract. During the MINOS campaign in August 2001 comprehensive two-dimensional gas chromatography (GCĂGC) was applied to the in situ measurements of atmospheric volatile organic compounds (VOCs) at the Finokalia ground station, Crete. The measurement system employs a thermal desorption unit for on-line sampling and injection, and a GCĂGC separation system equipped with a flame ionization detector (FID) for detection. The system was optimized to resolve C7 â C14 organic components. Two-dimensional chromatograms from measurements of Finokalia air samples show several hundred wellseparated peaks. To facilitate peak identification, cartridge samples collected at Finokalia were analyzed using the same GCĂGC system coupled with a time-of-flight mass spectrometer (TOF-MS). The resulting mass spectra were deconvoluted and compared to spectra from a database for tentative peak identification. About 650 peaks have been identified in the two-dimensional plane, with significant signal/noise ratios (>100) and high spectra similarities (>800). By comparing observed retention indices with those found in the literature, 235 of the identifications have been confirmed. 150 of the confirmed compounds show up in the C7 â C14 range of the chromatogram from the in situ measurement. However, at least as many peaks remain unidentified. For quantification of the GCĂGC measurements, peak volumes of measured compounds have been integrated and externally calibrated using a standard gas mixture.
Compilation and R-matrix analysis of Big Bang nuclear reaction rates
We use the R-matrix theory to fit low-energy data on nuclear reactions
involved in Big Bang nucleosynthesis. A special attention is paid to the rate
uncertainties which are evaluated on statistical grounds. We provide S factors
and reaction rates in tabular and graphical formats.Comment: 40 pages, accepted for publication at ADNDT, web site at
http://pntpm3.ulb.ac.be/bigban
Five-body resonances of 8He using the complex scaling method
The 0+ states of 8He are studied in a five-body 4He+n+n+n+n cluster model.
Many-body resonances are treated on the correct boundary condition as Gamow
states using the complex scaling method. The 0+_2 state of 8He is predicted as
a five-body resonance in the excitation energy of 6.3 MeV with a width of 3.2
MeV, which mainly has a (p_{3/2})^2(p_{1/2})^2 configuration. In this state,
number of the 0+ neuron pair shows almost two, which is different from the
ground state having a large amount of the 2+ pair component. The monopole
transition of 8He from the ground state into the five-body unbound states is
also evaluated. It is found that the 7He+n component mostly exhausts the
strength, while the 0+_2 contribution is negligible. The final states are
dominated by 6He+n+n, not 4He+n+n+n+n. The results indicate the sequential
breakup process of 8He to 7He+n to 6He+n+n by the monopole excitation.Comment: 6 pages, 6 figures, table I is updated for the experimental value
Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements
We improve Standard Big Bang Nucleosynthesis (SBBN) calculations taking into
account new nuclear physics analyses (Descouvemont et al. 2003). Using a
Monte-Carlo technique, we calculate the abundances of light nuclei versus the
baryon to photon ratio.The results concerning omegab are compared to relevant
astrophysical and cosmological observations. Consistency between WMAP, SBBN
results and D/H data strengthens the deduced baryon density and has interesting
consequences on cosmic chemical evolution. A significant discrepancy between
the calculated Li-7 deduced from WMAP and the Spite plateau is clearly
revealed. To explain this discrepancy three possibilities are invoked :
uncertainties on the Li abundance, surface alteration of Li in the course of
stellar evolution or poor knowledge of the reaction rates related to Be-7
destruction. In particular, the possible role of the up to now neglected
Be-7(d,p)2He-4 and Be-7(d,alpha)Li5 reactions is considered. The impressive
advances in CMB observations provide a strong motivation for more efforts in
experimental nuclear physics and high quality spectroscopy to keep BBN in pace.Comment: accepted in ApJ, 22 pages, 5 figure
Coupled-channel effective field theory and proton-Li scattering
We apply the renormalisation group (RG) to analyse scattering by short-range
forces in systems with coupled channels. For two S-wave channels, we find three
fixed points, corresponding to systems with zero, one or two bound or virtual
states at threshold. We use the RG to determine the power countings for the
resulting effective field theories. In the case of a single low-energy state,
the resulting theory takes the form of an effective-range expansion in the
strongly interacting channel. We also extend the analysis to include the
effects of the Coulomb interaction between charged particles. The approach is
then applied to the coupled Li and Be channels which couple to
a state of Be very close to the Be threshold. At
next-to-leading order, we are able to get a good description of the Li
phase shift and the Be(n,p)Li cross section using four parameters.
Fits at one order higher are similarly good but the available data are not
sufficient to determine all five parameters uniquely.Comment: 22 pages, 2 figures, RevTeX4, typos corrected, accepted for
publication in European Physical Journal
A Bitter Pill: The Primordial Lithium Problem Worsens
The lithium problem arises from the significant discrepancy between the
primordial 7Li abundance as predicted by BBN theory and the WMAP baryon
density, and the pre-Galactic lithium abundance inferred from observations of
metal-poor (Population II) stars. This problem has loomed for the past decade,
with a persistent discrepancy of a factor of 2--3 in 7Li/H. Recent developments
have sharpened all aspects of the Li problem. Namely: (1) BBN theory
predictions have sharpened due to new nuclear data, particularly the
uncertainty on 3He(alpha,gamma)7Be, has reduced to 7.4%, and with a central
value shift of ~ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic
baryon density with an uncertainty reduced to 2.7%. (3) Observations of
metal-poor stars have tested for systematic effects, and have reaped new
lithium isotopic data. With these, we now find that the BBN+WMAP predicts 7Li/H
= (5.24+0.71-0.67) 10^{-10}. The Li problem remains and indeed is exacerbated;
the discrepancy is now a factor 2.4--4.3 or 4.2sigma (from globular cluster
stars) to 5.3sigma (from halo field stars). Possible resolutions to the lithium
problem are briefly reviewed, and key nuclear, particle, and astronomical
measurements highlighted.Comment: 21 pages, 4 figures. Comments welcom
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