Speaker
Description
A keV sterile neutrino ($\nu_s$) that mixes with active neutrinos ($\nu_a$) is a well-motivated warm dark matter candidate with rich cosmological and astrophysical implications. The production of such a particle in the early Universe typically relies on the existence of a large lepton asymmetry in the primordial plasma, which can however spoil the successful predictions of Big Bang Nucleosynthesis. In this talk, I present an alternative scenario in which active neutrinos couple to an oscillating condensate of a very light $L_\mu-L_\tau$ gauge field, which enables resonant $\nu_a-\nu_s$ oscillations in the early Universe. The resulting sterile neutrino abundance is consistent with the observed dark matter one while respecting X-ray constraints on $\nu_s\rightarrow\nu_a\,\gamma$ decays. As a side effect, potentially observable deviations in (atmospheric) neutrino oscillations can persist to the present.
