Maximal parameter space of sterile neutrino dark matter with lepton asymmetries

TL;DR

This paper explores the maximum parameter space for sterile neutrino dark matter considering lepton flavor asymmetries, deriving a semi-classical approach validated against quantum equations, and providing tools for future observational tests.

Contribution

It introduces a semi-classical Boltzmann equation for sterile neutrino production in the presence of lepton asymmetries, extending the viable parameter space and offering a computational framework.

Findings

Viable mixing angles extend up to two orders of magnitude for sterile neutrino masses up to 60 keV.

Broad prospects for detection in upcoming X-ray, CMB, and structure formation observations.

Validated semi-classical approach against quantum kinetic equations.

Abstract

We delineate the maximal parameter space of sterile neutrino dark matter in the presence of lepton flavor asymmetries. We focus on large flavor asymmetries with vanishing total lepton asymmetry, which are washed out by neutrino oscillations at MeV temperatures and hence are consistent with BBN and CMB constraints. We derive a semi-classical Boltzmann equation for sterile neutrinos applicable in this regime and validate it against quantum kinetic equations. For sterile neutrino masses up to 60 keV, the viable range of mixing angles extends by up to two orders of magnitude, with broad prospects for tests in forthcoming X-ray, CMB, and structure formation observations. We also release a public framework to compute the production of sterile neutrinos, and in particular their momentum distribution, enabling dedicated structure formation analyses.