Large Neutrino Asymmetry from TeV Scale Leptogenesis

TL;DR

This paper explores TeV scale leptogenesis scenarios that produce large neutrino asymmetries, which could be detected via future cosmological experiments and may help explain recent helium measurement anomalies.

Contribution

It demonstrates that TeV scale leptogenesis, especially of the 1→N type with N≥3, can generate the observed baryon and neutrino asymmetries simultaneously.

Findings

Large neutrino asymmetry (~10^{-2}) can be produced by TeV scale leptogenesis.

Such asymmetry can be probed by future CMB experiments.

Low scale leptogenesis offers potential laboratory detection prospects.

Abstract

We study a class of leptogenesis scenarios with decay or scattering being the source of lepton asymmetry, which can not only give rise to the observed baryon asymmetry in the universe but also can leave behind a large remnant neutrino asymmetry. Such large neutrino asymmetry can not only be probed at future cosmic microwave background (CMB) experiments but is also motivating due to its possible role in solving the recently reported anomalies in $^4{\rm He}$ measurements. Additionally, such large neutrino asymmetry also offers the possibility of cogenesis if dark matter is in the form of a sterile neutrino resonantly produced in the early universe via Shi-Fuller mechanism. Considering $1 \rightarrow 2, 1 \rightarrow 3$ as well as $2 \rightarrow 2$ processes to be responsible for generating the asymmetries, we show that only TeV scale leptogenesis preferably of $1 \rightarrow N \, (N \geq 3)$ type can generate the required lepton asymmetry around sphaleron temperature while also generating a large neutrino asymmetry $\sim \mathcal{O}(10^{-2})$ by the epoch of the big bang nucleosynthesis. While such low scale leptogenesis can have tantalising detection prospects at laboratory experiments, the indication of a large neutrino asymmetry provides a complementary indirect signature.