Anatomy of RHN DM relic in the vanilla scotogenic neutrino mass model

TL;DR

This work analyzes right-handed neutrino dark matter in the vanilla scotogenic model, incorporating self-annihilation, co-annihilation, conversion-driven dynamics, and freeze-in production to determine viable relic densities under neutrino, LFV, and collider constraints. The authors show that thermal DM is viable in the range $M_h/2 \lesssim M_{DM} \lesssim 2000$ GeV, while non-thermal (freeze-in) DM can occupy $0.1$ GeV to $1000$ GeV, with the conversion-driven mechanism playing a key role in depleting the relic across broad parameter space. Neutrino mass generation via one-loop diagrams fixes Yukawa couplings in relation to $\lambda_5$, and LFV constraints typically favor larger $\lambda_5$ (smaller Yukawas) or require balancing against co-annihilation, with direct detection remaining loop-suppressed and currently unconstraining. A distinctive collider signature is provided by displaced vertices from $\eta^+$ decays, offering a complementary probe alongside electroweak precision tests and Higgs invisible decay bounds. Overall, the paper demonstrates a rich, testable DM phenomenology in the scotogenic setup, highlighting regions accessible to future colliders and the importance of considering conversion-driven processes for accurate relic predictions.

Abstract

The scotogeneic neutrino mass models are very popular choices to generate light neutrino masses via radiative mechanism. In these models, the particles running in the loop are distinguished from the standard model due to an imposed $\mathcal{Z}_2$ symmetry under which the loop particles are odd. Therefore, the lightest particle running in the loop can be a viable dark matter candidate. In this paper, we revisit the minimal scotogenic neutrino mass model and study the anatomy of right handed neutrino (RHN) DM relic, taking into account contributions from self-annihilation, co-annihilation, conversion-driven processes, as well as production via the freeze-in mechanism. We impose the constraints from direct detection and collider searches of DM including anomalous magnetic moment of muon, charged lepton flavor violation and low-energy neutrino oscillation data to show that the lightest RHN can be a viable DM in the mass range: $M_{h}/2\lesssim M_{\rm DM}\lesssim2000 {\rm GeV}$ (thermal DM) and $0.1 ~{\rm GeV}\lesssim M_{\rm DM}\lesssim 1000 {\rm GeV}$ (non-thermal DM), where $M_h$ denotes the Standard Model Higgs mass and $M_{\rm DM}$ is the RHN dark matter mass. We also find the displaced vertex signatures of long lived particles which can be probed at future colliders.

Figures (25)

• Figure 1: Behaviour of $|\lambda_{5}|$ vs $M_{\eta_R}$ for various $\lambda_{4}$ values. Left to the line of $M_{\eta_{\rm R}}=M_{\rm h}/2$ corresponds to the disallowed region from Higgs Invisible decay. Here we choose $\lambda_{4,5}<0$ and $\lambda_3=10^{-2}$.
• Figure 2: One loop realization of Majorana neutrino mass.
• Figure 3: Feynman diagram for charged lepton flavor violation.
• Figure 4: $y_{\mu1}$ is shown as a function of $M_{N_1}$, where the color band represents $|\lambda_5|$ values. As mentioned earlier, we have chosen $\lambda_{4,5}<0$.
• Figure 5: Relic density is shown as a function of DM mass. The various colored points represent the different values of $\lambda_4$ as given in figure inset. The $|\lambda_5|$ values are varied in the range $[10^{-10},4\pi]$ with $\lambda_5<0$. The value of $\lambda_3$ is fixed at 0.01. All the points satisfy the neutrino oscillation data, muon anomalous magnetic moment and cLFV. The barred region represents constraint from Higgs invisible decay. The colored shaded regions are ruled out by the bounds $M_{\eta_R}+M_{\eta_I}>M_Z$ and $M_{\eta^+}>100$ GeV for respective colored points.