Induced resonance makes light sterile neutrino Dark Matter cool

TL;DR

This paper introduces two novel mechanisms for producing sterile neutrino dark matter with lower temperatures and masses, evading X-ray constraints and aligning with structure formation, through resonance and scalar field effects.

Contribution

The paper presents new generation mechanisms involving scalar field oscillations and resonance effects for sterile neutrino dark matter production.

Findings

Resonant enhancement allows small mixing angle sterile neutrino production.

Produced dark matter spectrum is significantly cooler, enabling lower mass neutrinos.

Mechanisms are consistent with cosmic structure formation constraints.

Abstract

We describe two new generation mechanisms for Dark Matter composed of sterile neutrinos with ${\cal O}(1)$ keV mass. The model contains a light scalar field which coherently oscillates in the early Universe and modulates the Majorana mass of the sterile neutrino. In a region of model parameter space, the oscillations between active and sterile neutrinos are resonantly enhanced. This mechanism allows us to produce sterile neutrino DM with small mixing angle with active neutrinos, thus evading the X-ray constraints. At the same time the spectrum of produced DM is much cooler, than in the case of ordinary oscillations in plasma, opening a window of lower mass DM, which is otherwise forbidden by structure formation considerations. In other regions of the model parameter space, where the resonance does not appear, another mechanism can operate: large field suppresses the active-sterile oscillations, but instead sterile neutrinos are produced by the oscillating scalar field when the effective fermion mass crosses zero. In this case DM component is cold, and even 1 keV neutrino is consistent with the cosmic structure formation.