Shinning Light on Sterile Neutrino Portal Dark Matter from Cosmology and Collider

TL;DR

This paper explores how sterile neutrinos can connect dark matter and the standard model, analyzing cosmological and collider constraints on a specific dark sector scenario involving a dark scalar and fermion.

Contribution

It provides a comprehensive analysis of cosmological and collider constraints on a dark sector model with sterile neutrinos, focusing on delayed scalar decay and collider signatures.

Findings

Most parameter space with $m_N<m_W$ is accessible to future experiments.

Delayed decay of dark scalar affects cosmological observables.

Sterile neutrino can produce displaced vertices at colliders.

Abstract

Provided the dark sector consisted of a dark scalar $\phi$ and a dark fermion $\chi$ under an exact $Z_2$ symmetry, the sterile neutrino $N$ can act as the messenger between the dark sector and standard model via the Yukawa coupling $\lambda_{ds} \bar{\chi}\phi N$. In this paper, we focus on the specific scenario $m_N>m_\phi+m_\chi$ with $\chi$ being a FIMP dark matter. The decay width of dark scalar $\phi$ is doubly suppressed by the smallness of Yukawa coupling $\lambda_{ds}$ and mixing angle $\theta$. The delayed decay $\phi\to\chi\nu$ will have a great impact on cosmological observables such as the Big Bang Nucleosynthesis, the Cosmic Microwave Background anisotropy power spectra, the effective number of relativistic neutrino species $N_{\rm eff}$ and the energetic neutrino flux. Meanwhile, the sterile neutrino can generate displaced vertex signature at colliders when $m_N<m_W$. The dark scalar $\phi$ will also induce measurable Higgs invisible decay for relatively large quartic coupling. A comprehensive analysis of constraints from cosmology and collider is performed in this paper. We find that almost the whole parameter space with $m_N<m_W$ is under the reach of future experiments.