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Register a new userPrimordial Nucleosynthesis: an updated comparison of observational light nuclei abundances with theoretical predictions
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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.
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A new accurate evaluation of primordial light nuclei abundances is presented. The proton to neutron conversion rates have been corrected to take into account radiative effects, finite nucleon mass, thermal and plasma corrections. The theoretical uncertainty on 4He is so reduced to the order of 0.1%.
Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium, He3, He4 and Li7, during the first few minutes of the universe. This review concentrates on recent improvements in the measurement of the primordial (after BBN, and prior to modification) abundances of these nuclei. We mention improvement in the standard theory, and the non-standard extensions which are limited by the data. (abridged)
The ability to now make measurements of Be and B as well as put constraints on lisix abundances in metal-poor stars has led to a detailed reexamination of Big Bang Nucleosynthesis in the $Agroughly6$ regime. The nuclear reaction network has been significantly expanded with many new rates added. It is demonstrated that although a number of $A>7$ reaction rates are poorly determined, even with extreme values chosen, the standard homogeneous model is unable to produce significant yields (Be/H and B/H $<10^{-17}$ when $Ale7$ abundances fit) above $A=7$ and the liseven/lisix ratio always exceeds 500. We also preliminarily explore inhomogeneous models, such as those inspired by a first order quark-hadron phase transition, where regions with high neutron/proton ratios can allow some leakage up to $A>7$. However models that fit the $Ale7$ abundances still seem to have difficulty in obtaining significant $A>7$ yields.
Almost all chemical elements have been made by nucleosynthetic reactions in various kind of stars and have been accumulated along our cosmic history. Among those elements, the origin of phosphorus is of extreme interest because it is known to be essential for life such as we know on Earth. However, current models of (Galactic) chemical evolution under-predict the phosphorus we observe in our Solar System. Here we report the discovery of 15 phosphorus-rich stars with unusual overabundances of O, Mg, Si, Al, and Ce. Phosphorus-rich stars likely inherit their peculiar chemistry from another nearby stellar source but their intriguing chemical abundance pattern challenge the present stellar nucleosynthesis theoretical predictions. Specific effects such as rotation or advanced nucleosynthesis in convective-reactive regions in massive stars represent the most promising alternatives to explain the existence of phosphorus-rich stars. The phosphorus-rich stars progenitors may significantly contribute to the phosphorus present on Earth today.
We have modified the standard code for primordial nucleosynthesis to include the effect of the slight heating of neutrinos by $e^pm$ annihilations. There is a small, systematic change in the $^4$He yield, $Delta Y simeq +1.5times 10^{-4}$, which is insensitive to the value of the baryon-to-photon ratio $eta$ for $10^{-10}la eta la 10^{-9}$. We also find that the baryon-to-photon ratio decreases by about 0.5% less than the canonical factor of 4/11 because some of the entropy in $e^pm$ pairs is transferred to neutrinos. These results are in accord with recent analytical estimates.
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