Updated BBN Bounds on Hadronic Injection in the Early Universe: The Gravitino Problem

TL;DR

This paper refines constraints on long-lived particles' hadronic decays in the early universe, especially gravitinos, affecting Big Bang Nucleosynthesis predictions and setting bounds on reheating temperature.

Contribution

It provides updated bounds on hadronic injection effects during BBN and applies these to the gravitino problem, improving previous constraints.

Findings

Hadronic decays significantly alter light element abundances.

New bounds on primordial long-lived particle abundances.

Reheating temperature constraints tighten for gravitino scenarios.

Abstract

Late-decaying particles naturally arise in many extensions of the Standard Model, directly impacting key cosmological processes in the early universe, such as Big Bang Nucleosynthesis (BBN). BBN studies often consider electromagnetic energy injection episodes only, but in practice long-lived particles are also amenable to hadronic decays. The latter can greatly alter the predicted abundances of light elements such as $\mathrm{D}/\mathrm{H}$, $Y_p$, ${}^3\mathrm{He}/\mathrm{D}$, and ${}^7\mathrm{Li}/\mathrm{H}$. Incorporating up-to-date measurements, we place constraints on the primordial abundance of long-lived particles as a function of their lifetime. Lastly, we apply our results to the gravitino problem and set bounds on the reheating temperature, which controls the gravitino primordial abundance.