Large Neutrino Asymmetry from TeV Scale Leptogenesis in the Light of Helium Anomaly

Motivated by the growing evidence for a large neutrino asymmetry in the early universe from the recent ${}^4\mathrm{H}\mathrm{e}$ measurements, we point out the class of leptogenesis scenarios with decay or scattering being the source of lepton asymmetry, simultaneously consistent with such a large neutrino asymmetry as well as the observed baryon asymmetry of the universe. Considering $1\to 2,1\to 3$ as well as $2\to 2$ processes to be responsible for generating the asymmetries, we show that only TeV scale leptogenesis preferably of $1\to N(N\ge 3)$ 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. This also offers the possibility of cogenesis if dark matter is in the form of a sterile neutrino resonantly produced in the early universe due to the presence of a large neutrino asymmetry. While such low scale leptogenesis has tantalising detection prospects at laboratory experiments, the indication of a large neutrino asymmetry provides a complementary indirect signature.