keV Neutrino Dark Matter in a Fast Expanding Universe

TL;DR

This paper explores keV neutrino dark matter within a minimal $U(1)_{B-L}$ extension, proposing a non-standard cosmological phase to reconcile relic abundance with observations.

Contribution

It introduces a non-standard cosmological history involving a scalar field to achieve the correct relic abundance of keV neutrino dark matter in a minimal gauge extension.

Findings

Non-standard cosmology can prevent overproduction of keV neutrino dark matter.

Constraints on $U(1)_{B-L}$ parameters are derived from relic abundance requirements.

KeV neutrino dark matter remains a viable candidate with specific cosmological conditions.

Abstract

We study the possibility of keV neutrino dark matter in the minimal $U(1)_{B-L}$ gauge extension of the standard model where three right handed neutrinos are automatically included due to the requirement of anomaly cancellations. Without considering extra additional particles or symmetries, we consider the lightest right handed neutrino to be in the keV mass range which is kinematically long lived. Due to gauge interactions, such a keV neutrino can be thermally produced in the early Universe followed by decoupling while being relativistic. The final relic abundance of such keV neutrino typically overclose the Universe requiring additional mechanism to bring it under observed limits. We propose a non-standard cosmological history where a scalar field $\phi$, that redshifts faster than radiation dominates the Universe prior to the radiation dominated era. We show that such a non-standard phase can keep the abundance of thermally generated keV neutrino dark matter within observed relic abundance. We constrain the non-standard phase, $U(1)_{B-L}$ parameters from these requirements and also briefly comment upon the observational aspects of such keV neutrino dark matter.