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Register a new userBig Bang Nucleosynthesis Initial Conditions: Revisiting Wagoner et al. (1967)
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Added by
Geraint F. Lewis Prof
Publication date
2021
fields
Physics
and research's language is
English
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We revisit Wagoner et al. (1967), a classic contribution in the development of Big Bang Nucleosynthesis. We demonstrate that it presents an incorrect expression for the temperature of the early universe as a function of time in the high temperature limit, $T gtrsim 10^{10}$K. As this incorrect expression has been reproduced elsewhere, we present a corrected form for the initial conditions required for calculating the formation of the primordial elements in the Big Bang.
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Primordial or Big Bang nucleosynthesis (BBN) is one of the three historical strong evidences for the Big-Bang model together with the expansion of the Universe and the Cosmic Microwave Background radiation (CMB). The recent results by the Planck mission have slightly changed the estimate of the baryonic density Omega_b, compared to the previous WMAP value. This article updates the BBN predictions for the light elements using the new value of Omega_b determined by Planck, as well as an improvement of the nuclear network and new spectroscopic observations. While there is no major modification, the error bars of the primordial D/H abundance (2.67+/-0.09) x 10^{-5} are narrower and there is a slight lowering of the primordial Li/H abundance (4.89^+0.41_-0.39) x 10^{-10}. However, this last value is still ~3 times larger than its observed spectroscopic abundance in halo stars of the Galaxy. Primordial Helium abundance is now determined to be Y_p = 0.2463+/-0.0003.
Rijal, et al. in their recent publication [Phys. Rev. Lett {bf 122}, 182701 (2019), arXiv:1808.07893], on Measurement of d + $^7$Be Cross Sections for Big-Bang Nucleosynthesis (BBN), misrepresent their result, they misrepresent previous work of Parker (72) and of Caughlan and Fowler (88), and quite possibly, contradicts the very BBN theory that has been established over the last few decades. This comment is intended to correct these misrepresentations and critically review their claims on BBN.
I review standard big bang nucleosynthesis and so
In the primordial Universe, neutrino decoupling occurs only slightly before electron-positron annihilations, leading to an increased neutrino energy density with order $10^{-2}$ spectral distortions compared to the standard instantaneous decoupling approximation. However, there are discrepancies in the literature on the impact it has on the subsequent primordial nucleosynthesis, in terms of both the magnitude of the abundance modifications and their sign. We review how neutrino decoupling indirectly affects the various stages of nucleosynthesis, namely, the freezing out of neutron abundance, the duration of neutron beta decay, and nucleosynthesis itself. This allows to predict the sign of the abundance variations that are expected when the physics of neutrino decoupling is taken into account. For simplicity, we ignore neutrino oscillations, but we conjecture from the detailed interplay of neutrino temperature shifts and distortions that their effect on final light element abundances should be subdominant.
We provide the most stringent constraint to date on possible deviations from the usually-assumed Maxwell-Boltzmann (MB) velocity distribution for nuclei in the Big-Bang plasma. The impact of non-extensive Tsallis statistics on thermonuclear reaction rates involved in standard models of Big-Bang Nucleosynthesis (BBN) has been investigated. We find that the non-extensive parameter $q$ may deviate by, at most, $|delta q|$=6$times$10$^{-4}$ from unity for BBN predictions to be consistent with observed primordial abundances; $q$=1 represents the classical Boltzmann-Gibbs statistics. This constraint arises primarily from the {em super}sensitivity of endothermic rates on the value of $q$, which is found for the first time. As such, the implications of non-extensive statistics in other astrophysical environments should be explored. This may offer new insight into the nucleosynthesis of heavy elements.
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