Updated constraint on a primordial magnetic field during big bang nucleosynthesis and a formulation of field effects

TL;DR

This paper establishes a new upper limit on primordial magnetic fields during big bang nucleosynthesis by comparing updated theoretical abundance calculations with observational data, incorporating precise field effects.

Contribution

It introduces a rigorous formulation of magnetic field effects on elemental abundances and updates the constraint on the primordial magnetic field strength.

Findings

Primordial magnetic field amplitude constrained to B(0)<1.5 micro G

Abundances of 3He and 6Li increase with field strength

Abundance of 7Li decreases with field strength

Abstract

A new upper limit on the amplitude of primordial magnetic field (PMF) is derived by a comparison between a calculation of elemental abundances in big bang nucleosynthesis (BBN) model and the latest observational constraints on the abundances. Updated nuclear reaction rates are adopted in the calculation. Effects of PMF on the abundances are consistently taken into account in the numerical calculation with the precise formulation of changes in physical variables. We find that abundances of 3He and 6Li increase while that of 7Li decreases when the PMF amplitude increases, in the case of the baryon-to-photon ratio determined from the measurement of cosmic microwave background radiation. We derive a constraint on the present amplitude of PMF, i.e., B(0)<1.5 micro G [corresponding to the amplitude less than 2.0x10^{11} G at BBN temperature of T=10^9 K] based on the rigorous calculation.