Cosmological solutions to the Lithium problem: Big-bang nucleosynthesis with photon cooling, $X$-particle decay and a primordial magnetic field

TL;DR

This paper explores combined cosmological solutions involving photon cooling, $X$-particle decay, and primordial magnetic fields to resolve the discrepancy between predicted and observed lithium abundances from Big Bang nucleosynthesis.

Contribution

It reanalyzes previous solutions and introduces a combined model with photon cooling, $X$-particle decay, and magnetic fields, constraining parameters to address the lithium problem.

Findings

Optimal parameter ranges for $X$-particles and magnetic fields identified.

Likelihood analysis shows combined solutions can resolve the lithium discrepancy.

Constraints on primordial magnetic field strength and $X$-particle properties obtained.

Abstract

The $^7$Li abundance calculated in BBN with the baryon-to-photon ratio fixed from fits to the CMB power spectrum is inconsistent with the observed lithium abundances on the surface of metal-poor halo stars. Previous cosmological solutions proposed to resolve this $^7$Li problem include photon cooling (possibly via the Bose-Einstein condensation of a scalar particle) or the decay of a long-lived $X-$particle (possibly the next-to-lightest supersymmetric particle). In this paper we reanalyze these solutions, both separately and in concert. We also introduce the possibility of a primordial magnetic field (PMF) into these models. We constrain the $X-$particles and the PMF parameters by the observed light element abundances using a likelihood analysis to show that the inclusion of all three possibilities leads to an optimum solution to the lithium problem. We deduce allowed ranges for the $X-$particle parameters and energy density in the PMF that can solve $^7$Li problem.