Radiative Neutrino Mass Generation and Dark Matter through Vector-like Leptons

TL;DR

The paper develops a three-loop radiative mechanism to generate neutrino masses while connecting to dark matter via two inert scalar doublets and a single generation of vector-like leptons with asymmetric Yukawa couplings: $m^{\nu}_{ab} \propto (g_a \tilde{g}_b + \tilde{g}_a g_b)$. The neutrino-mass matrix also depends on $\lambda_5 \propto m_H^2 - m_A^2$, $\lambda_7 \propto m_{H_1^+}^2 - m_{H_2^+}^2$, and a three-loop integral $I_{3L}$, with the lightest $Z_2$-odd scalar serving as dark matter; a single VLL suffices to produce three nondegenerate light-neutrino masses. The model is tested against dark matter relic density, direct-detection limits, neutrino masses and mixing, and charged-lepton flavor violation, notably $\mu \to e \gamma$, finding regions compatible with current bounds and providing testable predictions for upcoming experiments. Two benchmark points illustrate viable DM candidates (one with $H^0$ as DM and one with $A^0$ as DM), showing consistent relic density, suppressed direct-detection signals, and neutrino observables in agreement with NO data, while forecasting measurable LFV effects within near-future experimental reach.

Abstract

This study presents a radiative three-loop framework for neutrino mass generation, employing an asymmetric Yukawa coupling between two new scalar $SU(2)_L$ doublets and vector-like lepton doublets. Dark matter candidates arise from the scalar sector of one of the doublets and play a crucial role in the generation of neutrino masses through their nonzero scalar mixing. The singly charged scalar sector undergoes an analogous mixing structure. A single generation of vector-like leptons yields three nondegenerate neutrino masses as a consequence of the asymmetric Yukawa combinations entering the neutrino mass matrix. The model is tested against dark matter phenomenology, neutrino mass and mixing data, and the charged lepton flavor-violating process $μ\rightarrow e γ$, showing compatibility with current bounds and leading to experimentally accessible predictions.

Figures (8)

• Figure 1: 3-loop topologies for generating neutrino masses
• Figure 2: 3-loop integral $I_{3L}$ as a function of $m_E$ for two different set of masses and $\beta$ angles (scenarios). Points remarked in both curves are used in numerical analysis section as benchmark points.
• Figure 3: Left: Dark matter abundance for the CP-even scalar $H^0$ (green) and CP-odd scalar $A^0$ (blue). Right: Spin-independent dark matter-nucleon cross section as a function of DM mass for the $H^0$ (green) and $A^0$ (blue). Also shown are current bounds from XENONnT (dashed black) and LZ (dashed red), along with the neutrino floor for a xenon target (shaded gray).
• Figure 4: The DM relic density as a function of the Higgs-portal coupling $\lambda_L$ for the DM candidate $H^0$ (left) and $\lambda_A$ for the DM candidate $A^0$ (right).
• Figure 5: Predicted correlations between CP violating phases and mixing parameters of neutrinos for BP 1. The yellow star indicates the best-fitting point. Gray-shaded regions, excluded by cosmology, arise from the Planck constraint on the neutrino mass sum $\sum m_i$Planck:2018vyg. Shaded regions in the $m_\beta$ and $m_{\beta\beta}$ panels represent experimental limits from beta decay and $0\nu\beta\beta$ experiments.