Metastable GeV-scale particles as a solution to the cosmological lithium problem

TL;DR

This paper proposes that decay of GeV-scale metastable particles in the early universe can reduce primordial lithium abundance predictions, potentially resolving the longstanding cosmological lithium problem.

Contribution

It introduces new mechanisms involving GeV-scale metastable particles decaying into charged pions, kaons, or muons to reconcile BBN lithium predictions with observations, expanding beyond standard models.

Findings

Decay to charged pions and kaons effectively reduces lithium abundance.

Metastable vector/scalar particles in minimal extensions of the Standard Model can solve the lithium problem.

These particles may also explain cosmic ray anomalies and are testable in high-energy experiments.

Abstract

The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.