630 research outputs found
Primordial Nucleosynthesis in the New Cosmology
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB)
anisotropies independently predict the universal baryon density. Comparing
their predictions will provide a fundamental test on cosmology. Using BBN and
the CMB together, we will be able to constrain particle physics, and predict
the primordial, light element abundances. These future analyses hinge on new
experimental and observational data. New experimental data on nuclear cross
sections will help reduce theoretical uncertainties in BBN's predictions. New
observations of light element abundances will further sharpen BBN's probe of
the baryon density. Observations from the MAP and PLANCK satellites will
measure the fluctuations in the CMB to unprecedented accuracy, allowing the
precise determination of the baryon density. When combined, this data will
present us with the opportunity to perform precision cosmology.Comment: 3 pages, 1 figure, for Nuclei in the Cosmos VII proceedings to appear
in Nuclear Physics
Primordial Nucleosynthesis: an updated comparison of observational light nuclei abundances with theoretical predictions
An up to date review of Standard Big Bang Nucleosynthesis predictions vs the
astrophysical estimates of light nuclei abundances is here presented. In
particular the analysis reports the expected ranges for baryon fraction and
effective number of neutrinos as obtained by BBN only.Comment: 5 pages, 4 figures, to appear in the proceedings of NOW 200
Solution to Big-Bang Nucleosynthesis in Hybrid Axion Dark Matter Model
Following a recent suggestion of axion cooling of photons between the
nucleosynthesis and recombination epochs in the Early Universe, we investigate
a hybrid model with both axions and relic supersymmetric particles. In this
model we demonstrate that the 7Li abundance can be consistent with observations
without destroying the important concordance of deuterium abundance.Comment: 5 pages, 3 figure
Nucleosynthesis during the Merger of White Dwarfs and the Origin of R Coronae Borealis Stars
Many hydrogen deficient stars are characterised by surface abundance patterns
that are hard to reconcile with conventional stellar evolution. Instead, it has
been suggested that they may represent the result of a merger episode between a
helium and a carbon-oxygen white dwarf. In this Letter, we present a
nucleosynthesis study of the merger of a 0.4 M_sol helium white dwarf with a
0.8 M_sol carbon-oxygen white dwarf, by coupling the thermodynamic history of
Smoothed Particle Hydrodynamics particles with a post-processing code. The
resulting chemical abundance pattern, particularly for oxygen and fluorine, is
in qualitative agreement with the observed abundances in R Coronae Borealis
stars.Comment: 5 Pages, 2 figures. Accepted to Astrophysical Journal Letters;
http://stacks.iop.org/2041-8205/737/L3
The Nuclear Reactions in Standard BBN
Nowadays, the Cosmic Microwave Background (CMB) anisotropies studies
accurately determine the baryon fraction omega_b, showing an overall and
striking agreement with previous determinations of omega_b obtained from Big
Bang Nucleosynthesis (BBN). However, a deeper comparison of BBN predictions
with the determinations of the primordial light nuclides abundances shows
slight tensions, motivating an effort to further improve the accuracy of
theoretical predictions, as well as to better evaluate systematics in both
observations and nuclear reactions measurements. We present some results of an
important step towards an increasing precision of BBN predictions, namely an
updated and critical review of the nuclear network, and a new protocol to
perform the nuclear data regression.Comment: 4 pp.,4figs. Few typos corrected and updated refs. to match the
version appearing in the proceedings of Conference ``Nuclei in the Cosmos
VIII'', Vancouver, BC, Canada, 19-23 Jul 2004, published in Nucl. Phys.
Effect of quark-mass variation on big bang nucleosynthesis
We calculate the effect of variation in the light-current quark mass, ,
on standard big bang nucleosynthesis. A change in at during the era of
nucleosynthesis affects nuclear reaction rates, and hence primordial
abundances, via changes the binding energies of light nuclei. It is found that
a relative variation of provides better
agreement between observed primordial abundances and those predicted by theory.
This is largely due to resolution of the existing discrepancies for 7Li.
However this method ignores possible changes in the position of resonances in
nuclear reactions. The predicted 7Li abundance has a strong dependence on the
cross-section of the resonant reactions 3He(d,p)4He and t(d,n)4He. We show that
changes in at the time of BBN could shift the position of these
resonances away from the Gamow window and lead to an increased production of
7Li, exacerbating the lithium problem
Geophysical constraint on a relic background of the dilatons
According to a scenario in string cosmology, a relic background of light
dilatons can be a significant component of the dark matter in the Universe. A
new approach of searching for such a dilatonic background by observing Earth's
surface gravity was proposed in my previous work. In this paper, the concept of
the geophysical search is briefly reviewed, and the geophysical constraint on
the dilaton background is presented as a function of the strength of the
dilaton coupling, . For simplicity, I focus on massless dilatons and
assume a simple Earth model. With the current upper limit on , we obtain
the upper limit on the dimensionless energy density of the massless background,
, which is about one-order of
magnitude more stringent than the one from astrophysical observations, at the
frequency of 7 10 Hz. If the magnitude of is
experimentally found to be smaller than the current upper limit by one order of
magnitude, the geophysical upper limit on becomes less
stringent and comparable to the one obtained from the astrophysical
observations.Comment: 6 pages, Proceedings for the 8th Edoardo Amaldi Conference on
Gravitational Waves, 21-26 June, 2009, Columbia University, New York, US
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