Singlet Majorana fermion dark matter: a comprehensive analysis in effective field theory

TL;DR

This paper provides a comprehensive EFT analysis of singlet Majorana fermion dark matter, considering various operators and constraints, and explores the impact of CP violation on the viable parameter space and future detection prospects.

Contribution

It systematically studies the complete set of dimension-5 and dimension-6 operators for singlet Majorana fermion dark matter within an EFT framework, including CP violation effects.

Findings

CP-conservation restricts the parameter space significantly.

Including CP-violating operators enlarges the viable parameter space.

Future experiments could probe significant portions of the remaining parameter space.

Abstract

We explore a singlet Majorana fermion dark matter candidate using an effective field theory (EFT) framework, respecting the relations imposed by the standard model $SU(3)_C \times SU(2)_L \times U(1)_Y$ gauge invariance among different couplings. All operators of dimension-5 and dimension-6, forming a complete basis, are taken into account at the same time, keeping in view ultraviolet completions which can give rise to more than one operator at a time. If in addition CP-conservation is assumed, the remaining parameter space, where an EFT description is valid, is found to be rather restricted after imposing constraints from relic abundance, direct, indirect and collider searches. On including the CP-violating dimension-5 operator, $(\overline{\chi}i \gamma_5 \chi) (H^\dagger H)$, a significantly larger parameter space opens up. We use the profile likelihood method to map out the remaining landscape of such a DM scenario. The reach of future searches using ton-scale direct detection experiments, an $e^+ e^-$ collider like the proposed ILC and limits from future gamma-ray observations are also estimated.