Non-thermal processes in standard big bang nucleosynthesis: I. In-flight nuclear reactions induced by energetic protons

Abstract

The standard model of big bang nucleosynthesis (BBN) relies on a nuclear reaction network operating with thermal reactivities for Maxwellian plasma. In the primordial plasma, however, a number of non-thermal processes triggered by energetic particles of various origins can take place. In the present work we examine in-flight nuclear reactions induced in the plasma by MeV protons generated in D(d, p)T and 3He(d, p)4He fusions. We particularly focus on several low threshold endoergic processes. These are reactions omitted in the standard network—proton-induced break-ups of loosely bound D, 7Li, 7Be nuclei—and the 3H(p, n)3He charge-exchange reaction important for the interconversion of A = 3 nuclei in the early universe. It is found that the break-up processes in the plasma take the form of Maxwellian processes at temperatures T>70 keV, while in the lower temperature range they proceed as non-thermal reactions. It is shown that at T<70 keV the in-flight reaction channels can enhance the break-up reactivities by several orders of magnitude. The levels of these reactivities however remain insufficiently high to affect BBN kinetics and change the standard prediction of light element abundances. The abundances are found to be: Yp = 0.2457, D/H = 2.542 × 10−5, 3He/H = 1.004 × 10−5, 7Li/H = 4.444 × 10−10. Future steps in the study of non-thermal processes in the primordial plasma are briefly discussed.

New nuclear physics for big bang nucleosynthesis

“…This assertion was based on a paper by Dixit et al [36], which studied 9 Be(p, p), and which identified a strongly excited, and relatively narrow, state at 16.7 MeV. In that paper the possible structure of a narrow state at such high excitation is discussed, and is identified with earlier theoretical work [37] in which this state is suggested as having a structure of an s 1/2 neutron coupled to highly excited 2 + core states in 8 Be. Such states could only be ν…”

On nonthermal processes in the core of the Sun

“…We will describe the reverse (α, p) process (3) within the in-flight nuclear-reaction formalism used earlier to analyze nonthermal reactions in the early Universe [16] and in superdense laboratory plasmas [17]. The probability W α 14 N that, in the course of deceleration in the plasma, a fast alpha particle undergoes the reaction α…”

Standard big bang nucleosynthesis with a nonthermal reaction network

“…In a series of papers [16][17][18]20] we examined the mechanisms and rates of nonthermal processes naturally triggered in the BBN epoch by fast particles generated in the tðd; nÞ, dðd; nÞ 3 He, dðd; pÞt, and 3 Heðd; pÞ reactions. The present work follows up these studies, considering the influence of such processes on the primordial element production.…”

“…Let us consider effects caused by nonthermal neutrons (for charged-particle effects, see [16,18]). Reactions having a resonancelike behavior at suprathermal energies and threshold processes are most sensitive to fast neutrons in the plasma.…”

“…At the same time, however, some nonthermal processes can also occur in the early Universe. The most natural ones are inflight reactions induced by energetic particles during slowing down in the plasma [11,[16][17][18][19]. These particles are predominantly produced in the tðd; nÞ, dðd; nÞ 3 He, dðd; pÞt, and 3 Heðd; pÞ fusion reactions and may be considered as primordial isotropic ''cosmic rays.''…”