Majorana dark matter in a classically scale invariant model

TL;DR

This paper explores a scale-invariant extension of the Standard Model with a dark gauge symmetry, predicting stable Majorana fermions as dark matter candidates, and analyzes their relic abundance, detection prospects, and experimental constraints.

Contribution

It introduces a novel classically scale-invariant model with Majorana dark matter candidates and studies their phenomenology, including annihilation channels and experimental constraints.

Findings

Dark gauge boson must be heavier than 680 GeV.

Viable dark matter mass range is 470 GeV to a few TeV.

Potential for distinctive direct detection signals with two Majorana fermions.

Abstract

We analyze a classically scale invariant extension of the Standard Model with dark gauge $U(1)_X$ broken by doubly charge scalar $\Phi$ leaving a remnant $Z_2$ symmetry. Dark fermions are introduced as dark matter candidates and for anomaly reasons we introduce two chiral fermions. Due to classical scale invariance, bare mass term that would mix these two states is absent and they end up as stable Majorana fermions $N_1$ and $N_2$. We calculate cross sections for $N_aN_a \to \phi\phi$, $N_aN_a \to X^\mu \phi$ and $N_2N_2 \to N_1N_1$ annihilation channels. We put constraints to the model from the Higgs searches at the LHC, dark matter relic abundance and dark matter direct detection limits by LUX. The dark gauge boson plays a crucial role in the Coleman-Weinberg mechanism and has to be heavier then 680 GeV. The viable mass region for dark matter is from 470 GeV up to a few TeV. In the case when two Majorana fermions have different masses, two dark matter signals at direct detection experiments could provide a distinctive signature of this model.