Nuclear Reaction Uncertainties, Massive Gravitino Decays and the Cosmological Lithium Problem

TL;DR

This paper investigates how nuclear reaction rate uncertainties affect constraints on unstable particle decays during Big-Bang nucleosynthesis, focusing on gravitino decays and their potential to resolve the cosmological lithium problem.

Contribution

It identifies key nuclear reactions influencing light-element abundances and quantifies uncertainties, improving the understanding of gravitino decay effects on BBN.

Findings

Certain gravitino masses and abundances fit observed light-element data better.

Uncertainties in nuclear reaction rates significantly impact BBN predictions.

Re-evaluating lithium data and reaction rates could help solve the lithium problem.

Abstract

We consider the effects of uncertainties in nuclear reaction rates on the cosmological constraints on the decays of unstable particles during or after Big-Bang nucleosynthesis (BBN). We identify the nuclear reactions due to non-thermal hadrons that are the most important in perturbing standard BBN, then quantify the uncertainties in these reactions and in the resulting light-element abundances. These results also indicate the key nuclear processes for which improved cross section data would allow different light-element abundances to be determined more accurately, thereby making possible more precise probes of BBN and evaluations of the cosmological constraints on unstable particles. Applying this analysis to models with unstable gravitinos decaying into neutralinos, we calculate the likelihood function for the light-element abundances measured currently, taking into account the current experimental errors in the determinations of the relevant nuclear reaction rates. We find a region of the gravitino mass and abundance in which the abundances of deuterium, He4 and Li7 may be fit with chi^2 = 5.5, compared with chi^2 = 31.7 if the effects of gravitino decays are unimportant. The best-fit solution is improved to chi^2 ~ 2.0 when the lithium abundance is taken from globular cluster data. Some such re-evaluation of the observed light-element abundances and/or nuclear reaction rates would be needed if this region of gravitino parameters is to provide a complete solution to the cosmological Li7 problem.