Time of primordial Be-7 conversion into Li-7, energy release and doublet of narrow cosmological neutrino lines

TL;DR

This paper models the timing of primordial Be-7 decay into Li-7 during recombination, accounting for hyperfine structure, and predicts narrow neutrino doublet lines from this decay, providing insights into early universe element formation.

Contribution

It introduces a detailed calculation of Be-7 to Li-7 conversion timing considering hyperfine states and predicts associated neutrino spectral lines, advancing understanding of nucleosynthesis.

Findings

Timing of Be-7 to Li-7 conversion during recombination

Predicted energies and spectrum of neutrino doublet lines

Enhanced modeling of primordial element decay processes

Abstract

One of the important light elements created during the big bang nucleosynthesis is Be-7 which then decays to Li-7 by electron capture when recombination becomes effective but well before the Saha equilibrium recombination is reached. This means that Be-7 should wait until its recombination epoch even though the half-life of the hydrogenic beryllium atom is only 106.4 days. We calculate when the conversion from primordial Be-7 to Li-7 occurs taking into account the population of the hyperfine structure sublevels and solving the kinetic equations for recombination, photoionization and conversion rate. We also calculate the energies and the spectrum of narrow neutrino doublet lines resulting from Be-7 decay.