Effects of transient non-thermal particles on the big bang nucleosynthesis

TL;DR

This study explores how transient non-thermal particles during specific periods of Big Bang nucleosynthesis can influence primordial element abundances, identifying parameter ranges that align predictions with observations.

Contribution

It introduces a time-dependent Gaussian model for non-thermal particles' influence on BBN and systematically scans parameter space to find conditions matching observed element abundances.

Findings

Approximately 130 parameter sets yield consistent primordial abundances.

The magnitude of non-thermal effects varies widely, from 10^{-19} to 10^{-1}.

The temperature region around 3-4×10^8 K is crucial for reducing discrepancies.

Abstract

The effects of introducing a small amount of non-thermal distribution (NTD) of elements in big bang nucleosynthesis (BBN) are studied by allowing a fraction of the NTD to be time-dependent so that it contributes only during a certain period of the BBN evolution. The fraction is modeled as a Gaussian-shaped function of $\log(T)$, where $T$ is the temperature of the cosmos, and thus the function is specified by three parameters; the central temporal position, the width and the magnitude. The change in the average nuclear reaction rates due to the presence of the NTD is assumed to be proportional to the Maxwellian reaction rates but with temperature $T_{\rm NTD} \equiv \zeta T$, $\zeta$ being another parameter of our model. By scanning a wide four-dimensional parametric space at about half a million points, we have found about 130 points with $\chi^2< 1$, at which the predicted primordial abundances of light elements are consistent with the observations. The magnitude parameter $\varepsilon_0$ of these points turns out to be scattered over a very wide range from $\varepsilon_0 \sim 10^{-19}$ to $\sim 10^{-1}$, and the $\zeta$-parameter is found to be strongly correlated with the magnitude parameter $\varepsilon_0$. The temperature region with $0.3\times 10^9 \mbox{K} \lesssim T \lesssim 0.4\times 10^9 \mbox{K}$ or the temporal region $t\simeq 10^3$ s seems to play a central role in lowering $\chi^2$.