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arXiv · 2604.05282

Constraints on the Injection of Radiation in the Early Universe

Melissa Joseph·Jason Kumar·Pearl Sandick
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Abstract

We consider the generic injection of radiation (both dark and electromagnetic) during the epoch between big bang nucleosynthesis (BBN) and recombination. The contribution of the additional radiation to the number of effective neutrinos may be quite small in this scenario, since dark radiation and electromagnetic radiation provide contributions of opposite sign. However, the injection of electromagnetic radiation dilutes the baryon-to-entropy ratio, which is measured both at BBN and at recombination. As a result, this scenario is expected to be tightly constrained. Indeed, performing a numerical study, we find that the allowed amount of extra radiation may be no more than $\sim 25\%$ greater than in the case where it is assumed to be entirely dark radiation.

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Melissa Joseph, Jason Kumar, Pearl Sandick. 2026-04-07. Constraints on the Injection of Radiation in the Early Universe. https://arxiv.org/abs/2604.05282

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