Effects of transient nonthermal particles on the big bang nucleosynthesis

Abstract

The effects of introducing a small amount of nonthermal 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 [Formula: see text], where [Formula: see text] 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 [Formula: see text], [Formula: see text] 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 [Formula: see text], at which the predicted primordial abundances of light elements are consistent with the observations. The magnitude parameter [Formula: see text] of these points turns out to be scattered over a very wide range from [Formula: see text] to [Formula: see text], and the [Formula: see text]-parameter is found to be strongly correlated with the magnitude parameter [Formula: see text]. The temperature region with [Formula: see text] or the temporal region [Formula: see text][Formula: see text]s seems to play a central role in lowering [Formula: see text].