Flavour and precision probes of a class of scotogenic models

TL;DR

The paper analyzes a class of scotogenic models focusing on the $T1-2-A$ variant to study flavour and electroweak precision observables. It computes full next-to-leading order corrections to leptonic $H$ and $Z$ decays and re-evaluates the relative importance of $Z$-penguin versus $\\gamma$-penguin contributions under the evolving $\\Delta a_\\mu$ results. It also maps the impact on charged-lepton flavour-violating processes ($\\mu \to e \\\gamma$, $\\mu \to 3e$, and $\\mu{-}e$ conversion) and on EWPO, highlighting how a SM-like $\\Delta a_\\mu$ shifts correlations between observables. The findings show sizeable corrections to $Z$- and $H$-decays in certain parameter regions, making $Z/H \to \\mu\\mu$ and $\\tau\\tau$ key probes at current and future colliders such as FCC-ee. Overall, the work reinforces the appeal of the $T1-2-A$ framework as a link between radiative neutrino masses, dark matter, and leptogenesis, with precise EWPO and flavour measurements offering strong tests.

Abstract

We address the phenomenological impact of a well-motivated class of scotogenic models regarding flavour and electroweak precision observables. For the case of a ``T1-2-A'' variant, we carry out a full computation of the next-to-leading order corrections to leptonic Higgs and $Z$-boson decays. We revisit previously drawn conclusions on operator dominance and constraints on the parameter space in view of the evolution regarding $Δa_μ$. Finally, we consider the role of $H \to μμ$ decays (and other flavour conserving Higgs decays), as well as precision observables in probing this class of models at future colliders.

Figures (4)

• Figure 1: One-loop diagrams contributing to neutrino masses (in the interaction basis).
• Figure 2: Predicted rates for $\mu \to 3e$ (top) and $\mu -e$ conversion in nuclei (bottom), both versus BR($\mu \to e \gamma$). On the left panels, all displayed points lead to a SM-like $(g-2)_\mu$ (i.e. $\Delta a_\mu \approx 1.5\sigma$), while the right panels exhibit a significant NP contribution ($\Delta a_\mu \approx 4.2\sigma$). Red points denote exclusion due to conflict with dark matter constraints, grey points correspond to the violation of at least one phenomenological bound (flavour, EWPO) other than those under study; blue points are viable under all constraints but those under consideration. Full (dashed) lines correspond to current bounds (future sensitivity), with hatched areas already excluded.
• Figure 3: BR($Z \to \mu \mu$) as a function of the scalar trilinear coupling $\alpha$. Point-colour scheme as in Fig. \ref{['fig:Mu3e:Mu-e:mueg']}. From darker to lighter, the green bands denote current bounds at $1\sigma$, $2\sigma$ and $3\sigma$. The full orange line corresponds to the SM 2-loop prediction Dubovyk:2018rlg, while dashed grey lines denote future sensitivity at FCC-ee. The left (right) panel corresponds to a SM-like (NP-like) $(g-2)_\mu$.
• Figure 4: BR($H \to \mu \mu$) as a function of the lightest scalar mass, $M_{\phi_1}$, for a SM-like $(g-2)_\mu$ (left) and a significant tension ($\Delta a_\mu = 4.2 \sigma$, on the right). Line and colour code as in Fig. \ref{['fig:ZMuMu']}, with the full line denoting the SM prediction LHCHiggsCrossSectionWorkingGroup:2016ypw.