Sterile neutrino dark matter, neutrino secret self-interactions and extra radiation

Manibrata Sen

doi:10.1088/1742-6596/2156/1/012018

Abstract

keV scale sterile neutrinos are excellent warm dark matter candidates. In the early Universe, these can be produced from oscillations and scatterings of active neutrinos. However, in the absence of any new physics, this mechanism is in severe tension with observations from X-ray searches. In this work, we show that secret self-interactions of active neutrinos, mediated by a scalar, can efficiently produce these sterile neutrinos without being ruled out by X-ray observations. These neutrino self-interactions are also testable: for a mediator mass greater than a few MeV, these self-interactions can give signatures in laboratory based experiments, while for lighter mediators, there will be observable consequences for upcoming cosmology probes.1

Highlights

The presence of non-zero neutrino masses, confirmed by neutrino oscillation data, presents robust evidence of the existence of physics beyond the Standard Model (SM) of particle physics
We show that secret self-interactions of active neutrinos, mediated by a scalar, can efficiently produce these sterile neutrinos without being ruled out by X-ray observations
Characterized by a tiny mixing with the active neutrinos, these warm dark matter candidate (WDM) can be produced non-thermally due to active-sterile oscillations in the early Universe, as was shown by Dodelson and Widrow (DW) [1]

Summary

Introduction

The presence of non-zero neutrino masses, confirmed by neutrino oscillation data, presents robust evidence of the existence of physics beyond the Standard Model (SM) of particle physics. Characterized by a tiny mixing with the active neutrinos, these WDM can be produced non-thermally due to active-sterile oscillations in the early Universe, as was shown by Dodelson and Widrow (DW) [1]. Presence of a large lepton asymmetry is difficult to test, and, in general, difficult to explain, given the tiny baryon asymmetry. To this end, we propose a new experimentally testable way of producing the correct relic density in the Universe, without getting into trouble with astrophysical bounds [4, 5, 6]. These neutrino self-interactions are testable: for a mediator mass greater than a few MeV, these self-interactions can give signatures in laboratory based experiments, while for lighter mediators, this can modify the standard cosmology, and have observable consequences for upcoming cosmology probes

The Dodelson-Widrow mechanism

Non-standard neutrino self-interactions

10-4 BBN 10-5