Effects of transient nonthermal particles on the big bang nucleosynthesis

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 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-NTD equivalent to 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 epsilon(0) of these points turns out to be scattered over a very wide range from epsilon(0) similar to 10(-19) to similar to 10(-1), and the zeta-parameter is found to be strongly correlated with the magnitude parameter epsilon(0). The temperature region with 0.3 x 10(9)K less than or similar to T less than or similar to 0.4 x 10(9)K or the temporal region t similar or equal to 10(3) s seems to play a central role in lowering chi(2).