Antimatter Regions in the Early Universe and Big Bang Nucleosynthesis

TL;DR

This paper investigates how antimatter regions in the early universe affected big bang nucleosynthesis, constraining antimatter abundance based on observed element yields and exploring different annihilation scenarios.

Contribution

It provides a detailed analysis of how antimatter regions influence primordial element production and sets constraints on antimatter presence in the early universe.

Findings

Small antimatter regions reduce 4He yield due to neutron annihilation.

Large antimatter regions increase 3He yield through annihilation processes.

Multiple mechanisms contribute to 3He production, with varying survival rates.

Abstract

We have studied big bang nucleosynthesis in the presence of regions of antimatter. Depending on the distance scale of the antimatter region, and thus the epoch of their annihilation, the amount of antimatter in the early universe is constrained by the observed abundances. Small regions, which annihilate after weak freezeout but before nucleosynthesis, lead to a reduction in the 4He yield, because of neutron annihilation. Large regions, which annihilate after nucleosynthesis, lead to an increased 3He yield. Deuterium production is also affected but not as much. The three most important production mechanisms of 3He are 1) photodisintegration of 4He by the annihilation radiation, 2) pbar-4He annihilation, and 3) nbar-4He annihilation by "secondary" antineutrons produced in anti-4He annihilation. Although pbar-4He annihilation produces more 3He than the secondary nbar-4He annihilation, the products of the latter survive later annihilation much better, since they are distributed further away from the annihilation zone.