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

Understand

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.