Dark matter and scalar sector in a novel two-loop scotogenic neutrino mass model

TL;DR

The paper presents a $Q_6\times Z_2\times Z_4$-symmetric extension of the SM with four Higgs doublets and multiple singlets, incorporating three right-handed Majorana neutrinos to realize a two-loop radiative seesaw that yields active-neutrino masses. It achieves cobimaximal leptonic mixing and predicts a multi-component dark matter sector stabilized by preserved discrete symmetries, all while remaining compatible with quark masses and collider/dark-matter constraints. The scalar sector features one SM-like Higgs and several non-SM scalars, including a light non-SM state near $95$ GeV that could address the diphoton excess, and additional sub-TeV scalars potentially accessible at the LHC. A global numerical analysis shows viable regions that satisfy relic-density and direct-detection limits, with a best-fit scenario and distinctive predictions for the scalar spectrum and DM phenomenology, making the model testable at current and future experiments.

Abstract

We propose an extended $3+1$ Higgs doublet model where the Standard Model (SM) gauge structure is enhanced by the discrete symmetry $Q_6 \times Z_2 \times Z_4$, and the fermion content is extended with right-handed Majorana neutrinos. The scalar sector, besides four $SU(2)$ doublets, incorporates multiple gauge-singlet scalars. In our model, the tiny active neutrino masses arise from a novel radiative seesaw mechanism at two-loop level and the leptonic mixing features the cobimaximal mixing pattern compatible with neutrino oscillation experimental data. Along with this, the proposed model is consistent with SM quark masses and mixings as well as with the constraints arising from dark matter relic density and dark matter direct detection. Our analysis reveals that the best-fit point satisfying dark matter constraints yields a non-SM scalar with mass near $95$ GeV, which could be a possible candidate for the observed $95$ GeV diphoton excess. We further obtain other non SM scalars with masses at the subTeV scale which are within the LHC reach, while successfully complying with the experimental bounds arising from collider searches.

Figures (10)

• Figure 1: two-loop Feynman diagram contribution to neutrino masses.
• Figure 2: Correlation plots between mixing angles, effective Majorana mass, and sum of lightest neutrino masses.
• Figure 3: Correlation plot between mixing angles and CP violation phase, for different values of $\sin^2{ \if@compatibility \mathchar"0112 {} \mathchar"0112 }_{13}$.
• Figure 4: Correlation plots between the masses of the scalar sector, $R_{{ \if@compatibility \mathchar"010D {} \mathchar"010D }{ \if@compatibility \mathchar"010D {} \mathchar"010D }}$ and ${ \if@compatibility \mathchar"0114 {} \mathchar"0114 }_W$, considering low energies, considering ${ \if@compatibility \mathchar"0116 {} \mathchar"0116 }_1^2 =0$.
• Figure 5: Correlation plots between the masses of the scalar sector, $R_{{ \if@compatibility \mathchar"010D {} \mathchar"010D }{ \if@compatibility \mathchar"010D {} \mathchar"010D }}$ and ${ \if@compatibility \mathchar"0114 {} \mathchar"0114 }_W$, considering low energies, considering ${ \if@compatibility \mathchar"0116 {} \mathchar"0116 }_1^2 \not =0$.