40,507 research outputs found

### Coulomb screening in linear coasting nucleosynthesis

We investigate the impact of coulomb screening on primordial nucleosynthesis
in a universe having scale factor that evolves linearly with time. Coulomb
screening affects primordial nucleosynthesis via enhancement of thermonuclear
reaction rates. This enhancement is determined by the solving Poisson equation
within the context of mean field theory (under appropriate conditions during
the primordial nucleosynthesis). Using these results, we claim that the mean
field estimates of coulomb screening hardly affect the predicted element
abundances and nucleosynthesis parameters$, \{\eta_9,\xi_e\}$. The deviations
from mean field estimates are also studied in detail by boosting genuine
screening results with the screening parameter ($\omega_s$). These deviations
show negligible effect on the element abundances and on nucleosynthesis
parameters. This work thus rules out the coulomb screening effects on
primordial nucleosynthesis in slow evolving models and confirms that
constraints in ref.[7] on nucleosynthesis parameters remain unaltered.Comment: 14 pages,11 figur

### Inhomogeneous Big-Bang Nucleosynthesis in Light of Recent Observations

We consider inhomogeneous big bang nucleosynthesis in light of the present
observational situation. Different observations of He-4 and D disagree with
each other, and depending on which set of observations one uses, the estimated
primordial He-4 corresponds to a lower baryon density in standard big bang
nucleosynthesis than what one gets from deuterium. Recent Kamiokande results
rule out a favorite particle physics solution to this tension between He-4 and
D. Inhomogeneous nucleosynthesis can alleviate this tension, but the more
likely solution is systematics in the observations. The upper limit to Omega_b
from inhomogeneous nucleosynthesis is higher than in standard nucleosynthesis,
given that the distance scale of the inhomogeneity is near the optimal value,
which maximizes effects of neutron diffusion. Possible sources of baryon
inhomogeneity include the QCD and electroweak phase transitions. The distance
scale of the inhomogeneities arising from the electroweak transition is too
small for them to have a large effect on nucleosynthesis, but the effect may
still be larger than some of the other small corrections recently incorporated
to SBBN codes.Comment: 12 pages, 8 figures, REVTe

### Primordial Nucleosynthesis

Primordial nucleosynthesis, or Big-Bang Nucleosynthesis (BBN), is one of the
three evidences for the Big-Bang model, together with the expansion of the
Universe and the Cosmic Microwave Background. There is a good global agreement
over a range of nine orders of magnitude between abundances of 4He, D, 3He and
7Li deduced from observations, and calculated in primordial nucleosynthesis.
This comparison was used to determine the baryonic density of the Universe. For
this purpose, it is now superseded by the analysis of the Cosmic Microwave
Background (CMB) radiation anisotropies. However, there remain, a yet
unexplained, discrepancy of a factor 3-5, between the calculated and observed
lithium primordial abundances, that has not been reduced, neither by recent
nuclear physics experiments, nor by new observations. We review here the
nuclear physics aspects of BBN for the production of 4He, D, 3He and 7Li, but
also 6Li, 9Be, 11B and up to CNO isotopes. These are, for instance, important
for the initial composition of the matter at the origin of the first stars.
Big-Bang nucleosynthesis, that has been used, to first constrain the baryonic
density, and the number of neutrino families, remains, a valuable tool to probe
the physics of the early Universe, like variation of "constants" or alternative
theories of gravity.Comment: Invited Plenary Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS

### Recommendations for Monte Carlo nucleosynthesis sampling (Research Note)

Context: Recent reaction rate evaluations include reaction rate uncertainties
that have been determined in a statistically meaningful manner. Furthermore,
reaction rate probability density distributions have been determined and
published in the form of lognormal parameters with the specific goal of
pursuing Monte Carlo nucleosynthesis studies.
Aims: To test and assess different methods of randomly sampling over reaction
rate probability densities and to determine the most accurate method for
estimating elemental abundance uncertainties.
Methods: Experimental Monte Carlo reaction rates are first computed for the
22Ne+alpha, 20Ne(p,g)21Na, 25Mg(p,g)26Al, and 18F(p,alpha)15O reactions, which
are used to calculate reference nucleosynthesis yields for 16 nuclei affected
by nucleosynthesis in massive stars and classical novae. Five different methods
of randomly sampling over these reaction rate probability distributions are
then developed, tested, and compared with the reference nucleosynthesis yields.
Results: Given that the reaction rate probability density distributions can
be described accurately with a lognormal distribution, Monte Carlo
nucleosynthesis variations arising from the parametrised estimates for the
reaction rate variations agree remarkably well with those obtained from the
true rate samples. Most significantly, the most simple parametrisation agrees
within just a few percent, meaning that Monte Carlo nucleosynthesis studies can
be performed reliably using lognormal parametrisations of reaction rate
probability density functions.Comment: 6 pages, 3 figures. Accepted to Astronomy & Astrophysics as a
Research Not

- â€¦