Freeze-in Production of Sterile Neutrino Dark Matter in U(1)$_{\rm B-L}$ Model

TL;DR

This paper investigates non-thermal sterile neutrino dark matter production in the U(1)$_{ m B-L}$ model, highlighting the role of $W^\pm$ decay and solving Boltzmann equations to match observed relic density.

Contribution

It demonstrates that $W^\pm$ decay can be a dominant production mode for sterile neutrino dark matter in the U(1)$_{ m B-L}$ model, extending the understanding of non-thermal DM origins.

Findings

$W^\pm$ decay can dominate sterile neutrino production.

Coupled Boltzmann equations effectively model relic density.

Framework applicable to other models with extra neutral gauge bosons.

Abstract

With the advent of new and more sensitive direct detection experiments, scope for a thermal WIMP explanation of dark matter (DM) has become extremely constricted. The non-observation of thermal WIMP in these experiments has put a strong upper bound on WIMP-nucleon scattering cross section and within a few years it is likely to touch the neutrino floor. Hence in all probability, DM may have some non-thermal origin. In this work we explore in detail this possibility of a non-thermal sterile neutrino DM within the framework of U(1)$_{\rm B-L}$ model. The U(1)$_{\rm B-L}$ model on the other hand is a well-motivated and minimal way of extending the standard model so that it can explain the neutrino masses via Type-I see-saw mechanism. We have shown, besides explaining the neutrino mass, it can also accommodate a non-thermal sterile neutrino DM with correct relic density. In contrast with the existing literature, we have found that $W^\pm$ decay can also be a dominant production mode of the sterile neutrino DM. To obtain the comoving number density of dark matter, we have solved here a coupled set of Boltzmann equations considering all possible decay as well as annihilation production modes of the sterile neutrino dark matter. The framework developed here though has been done for a U(1)$_{\rm B-L}$ model, can be applied quite generally for any models with an extra neutral gauge boson and a fermionic non-thermal dark matter.