Bounds on long-lived charged massive particles from Big Bang nucleosynthesis

TL;DR

This paper investigates how long-lived charged massive particles (CHAMPs) affect Big Bang nucleosynthesis, providing bounds on their abundance and highlighting the potential for tighter constraints with future reaction rate data.

Contribution

It offers detailed bounds on CHAMP abundances during BBN, incorporating all known effects and a comprehensive Monte Carlo analysis, improving understanding of their cosmological impact.

Findings

Conservative bounds on CHAMP abundance are close to those for neutral particles.

Early Li6 production estimates are overestimated by a factor of ~10 using Saha approximation.

Future precise reaction rate measurements could significantly tighten CHAMP abundance limits.

Abstract

The Big Bang nucleosynthesis (BBN) in the presence of charged massive particles (CHAMPs) is studied in detail. All currently known effects due to the existence of bound states between CHAMPs and nuclei, including possible late-time destruction of Li6 and Li7 are included. The study sets conservative bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It is stressed that the production of Li6 at early times T ~ 10keV is overestimated by a factor ~ 10 when the approximation of the Saha equation for the He4 bound state fraction is utilised. To obtain conservative limits on the abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs, varying reaction rates of nineteen different reactions, is performed (see attached erratum, however). The analysis yields the surprising result that except for small areas in the particle parameter space conservative constraints on the abundance of decaying charged particles are currently very close to those of neutral particles. It is shown that, in case a number of heretofore unconsidered reactions may be determined reliably in future, it is conceivable that the limit on CHAMPs in the early Universe could be tightened by orders of magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates are employed.