Big Bang Nucleosynthesis and the Neutrino-Extended Standard Model Effective Field Theory

TL;DR

This paper investigates how GeV-scale heavy neutral leptons influence Big Bang nucleosynthesis within the $ u$SMEFT framework, providing bounds that complement collider and decay experiments, and identifying future experimental targets.

Contribution

It introduces BBN constraints on the $ u$SMEFT cut-off scale for HNLs above 100 MeV, linking cosmological and laboratory bounds in a novel way.

Findings

BBN constrains the $ u$SMEFT cut-off scale for HNLs above 100 MeV.

BBN bounds complement collider and decay experiment constraints.

Identifies target regions for future laboratory searches.

Abstract

We study the impact of light GeV-scale heavy neutral leptons (HNLs) on Big Bang nucleosynthesis (BBN) in the neutrino-extended Standard Model Effective Field Theory ($\nu$SMEFT). We show that, based on very general considerations, BBN constraints complement laboratory searches at colliders, beam dumps, and neutrinoless double beta decay, by providing an upper bound on the cut-off scale of the effective field theory for HNL masses above $\sim$100 MeV. We identify target regions for future laboratory probes of the $\nu$SMEFT parameter space that is bounded from above and below.