ANALYSIS OF SUPRATHERMAL NUCLEAR EFFECTS IN THE STANDARD MODEL OF BIG BANG NUCLEOSYNTHESIS

Abstract

Energetic reaction-produced particles in the primordial plasma form the groups of suprathermal plasma species (n, p, t, 3He, α) that can induce a number of nonthermal nuclear reactions. To clarify their role in standard big bang nucleosynthesis (BBN), we examine the properties of these groups and determine their influence on individual reactions as well as BBN kinetics as a whole. It is found that the partial fraction η' c of fast charged particles c in the total c-component of the plasma is less than 10–6. However, their temperatures T' c appreciably exceed the universe temperature in the BBN epoch and reach the MeV region. The most abundant suprathermal species are neutron (0.01% of the total free neutron density). It is demonstrated that the fast particles can essentially enhance endoergic processes. However, they do not change the rates of main exoergic reactions and thereby cannot affect the abundances of primordial D, 3He, 4He, 7Li (only a tiny reduction of 7Li by 0.02% is obtained). Estimations show that positive impacts on the D and 7Li abundances might appear if the fast proton or neutron fraction would reach 10–6 or 10–2, respectively. Such an amount of fast protons is impossible to acquire by standard BBN mechanisms. As for fast neutrons, a fully realistic consideration of neutronic processes may in principle approach (η' n , T' n ) to the values needed to obtain a signature of suprathermal effect. This gives an impetus for such study.