Flavor Imprints on Novel Low Mass Dark Matter

Abstract

We present a Majorana scotogenic-like loop framework in which neutrino mass generation and dark matter stability are intrinsically connected to the breaking of the discrete flavor symmetry $A_4$. This breaking leads to the emergence of the scoto-seesaw mechanism and a $Z_2$ symmetry. This naturally explains the solar and atmospheric mass-squared differences, $Δm_{sol}^{2}$ and $Δm_{atm}^{2}$, while simultaneously ensuring dark matter stability. Our model accommodates normal ordering of neutrino masses, with a generalized $μ$-$τ$ reflection symmetry shaping the structure of leptonic mixing and a lower limit on the lightest neutrino mass. Moreover, the model provides predictions for the octant of $θ_{23}$ and a strong correlation between $Δm_{sol}^{2}$ and $Δm_{atm}^{2}$. This correlation puts a lower bound on the fermionic DM mass. In contrast, scalar dark matter remains viable over a broad mass spectrum. A notable feature is that the low mass regime ($\sim 15$ GeV onwards) survives owing to the presence of efficient co-annihilation channels, which are typically absent in the Majorana scotogenic scenario. Additionally, the model aligns with current and future limits from lepton flavor violation experiments.

Figures (10)

• Figure 1: Neutrino mass generation through the scotogenic-like loop.
• Figure 2: The emergence of the hybrid scoto-seesaw mass mechanism from the breaking $A_4 \to Z_2$ has been shown. The left diagram represents loop before SSB where $A_4$ triplets are running in the loop. After SSB, tree-level seesaw and loop-level scoto diagram have been shown in the right panel. The particles running in the loop (right bottom) are $Z_2$ odd, and the lightest of them serves as a viable DM candidate.
• Figure 3: The correlation between atmospheric mixing angle $\theta_{23}$ and ratio of Yukawa couplings $y_2/y_3$.
• Figure 4: Left: Prediction of generalized $\mu$–$\tau$ reflection symmetry, showing a robust correlation between the CP-violating phase $\delta_{CP}$ and the mixing angle $\theta_{23}$. The intersection of the dashed black lines corresponds to the exact $\mu$–$\tau$ reflection symmetry prediction. Right: Correlation of the lightest neutrino mass, $m_1 = m_{\rm{lightest}}$ with the mixing angle $\theta_{12}$. The allowed range of $\theta_{12}$ imposes a lower bound on the lightest neutrino mass.
• Figure 5: The correlation between two mass-squared differences, $\Delta m^2_{\rm {sol}}$ and $\Delta m^2_{\rm {atm}}$ for the fermionic DM (left) and scalar DM (right) scenarios. The color bar on the right indicates the variation of the fermion mass $M$ for both cases. The yellow region corresponding to $M \gtrsim 10^4$ GeV extends up to the seesaw scale ($10^{12}$ GeV), beyond which the Yukawa couplings reach their perturbativity limit. Only points within the intersection of the vertical and horizontal green bands satisfy both mass-squared difference constraints.