Marco Hufnagel

TL;DR: In this article, the authors study generic constraints from Big Bang Nucleosynthesis on such a setup, with a particular emphasis on MeV-scale particles which are neither fully relativistic nor non-relativistic during all times relevant for Big Bang nucleosynthesis, and apply their results to a simple model of selfinteracting dark matter with a light scalar mediator.

TL;DR: In this article, a detailed evaluation of BBN bounds on the annihilation cross section of dark matter with a mass $1\,\text{MeV}, m_\chi \lesssim 1\, \text{GeV} was performed.

TL;DR: In this paper, the case of MeV-scale particles decaying into dark radiation was considered and it was shown that these particles are neither fully relativistic nor non-relativistic during all temperatures relevant to Big Bang Nucleosynthesis.

Abstract: Axion-like particles with masses in the keV-GeV range have a profound impact on the cosmological evolution of our Universe, in particular on the abundance of light elements produced during Big Bang Nucleosynthesis. The resulting limits are complementary to searches in the laboratory and provide valuable additional information regarding the validity of a given point in parameter space. A potential drawback is that altering the cosmological history may potentially weaken or even fully invalidate these bounds. The main objective of this article is therefore to evaluate the robustness of cosmological constraints on axion-like particles in the keV-GeV region, allowing for various additional effects which may weaken the bounds of the standard scenario. Employing the latest determinations of the primordial abundances as well as information from the cosmic microwave background we find that while bounds can indeed be weakened, very relevant robust constraints remain.

TL;DR: The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions, referred to as heavy neutral leptons (HNLs) as discussed by the authors .