Lepton Flavor Violating Higgs Decays in a Minimal Doublet Left-Right Symmetric Model with an Inverse Seesaw

TL;DR

This work analyzes lepton flavor violation in a minimal Doublet Left-Right Symmetric Model augmented by an inverse seesaw, where the scalar sector and a high-scale $v_R$ enable TeV-scale heavy neutrinos and sizeable active-sterile mixing. Neutrino masses are generated via the inverse seesaw, and LFV observables are computed at one loop, including contributions from $W'$, $H_R^{\pm}$, and heavy neutrinos to both $\ell\to\ell'\gamma$ and $h^{SM}\to\ell_a\ell_b$. The authors implement the model with SARAH/SPheno, perform a multi-objective MCMC scan constrained by the SM Higgs mass and collider bounds, and identify viable regions where $\mathcal{BR}(h^{SM}\to\mu\tau)$ and $\mathcal{BR}(\mu\to e\gamma)$ are within current or projected experimental reach. The results show LFV Higgs decays could be observable at HL-LHC or a future muon collider, providing a window into the flavor structure of neutrino mass generation beyond the Standard Model. Overall, the paper demonstrates that the DLRSM with ISS can reconcile neutrino data with detectable LFV signals while remaining consistent with collider constraints.

Abstract

In this study, we analyse the lepton flavor violation (LFV) decays within the framework of the Doublet Left-Right Symmetric model (DLRSM), based on the gauge group SU\left(2\right)_{L}\otimes SU\left(2\right)_{R}\otimes U\left(1\right)_{B-L}. The model features an extended gauge and scalar sector, including a bidoublet and two doublets which induce new charged currents interactions. Spontaneous Symmetry Breaking (SSB) occurs in two stages, introducing a new scale associated with the vacuum expectation value (VEV) of the right-handed doublet v_{R} assumed to lie above the electroweak scale. Neutrino masses are generated via the inverse seesaw mechanism, allowing sizeable mixing between active and sterile neutrinos. We diagonalize the full neutrino mass matrix and express the mixing in terms of physical parameters. We compute the branching ratios for LFV Higgs decays as functions of the heavy neutrino mass scale. Our numerical analysis incorporates current experimental bounds and projected sensitivities, highlighting viable regions of parameter space where LFV signals could be observed at future colliders.

Figures (5)

• Figure 1: One loop topologies in the LFVHD, with the conventions of momentum, label of vertexes and masses of each particle in the loop.
• Figure 2: Behaviour of $\mathcal{BR}\left(h\to\ell_{a}\ell_{b}\right)$ left panel and $\mathcal{BR}\left(\ell_{b}\to a\ell_{a}\right)$ right panel. On left panel we fix $Y_{R}=0.1$, $\mu_{X}=10^{-3}$ GeV in right panel $Y_{R}=1$ and $\mu_{X}=10^{-6}$ GeV
• Figure 3: In this figure we show the behavior of $\mathcal{BR}\left(\mu\to e\gamma\right)$as a function of (a) $v_{R}$ and we fix $\mu_{X}=10^{-6}$ GeV, for different values of YR and (b) $v_{R}$ and $Y_{R}=1$ and $\mu_{X}$variable.
• Figure 4: In this figure we show the behavior of $\mathcal{BR}\left(h\to\mu\tau\right)$as a function of (a) $v_{R}$ and we fix $\mu_{X}=10^{-6}$ GeV, for different values of $Y_{R}$ and (b) $v_{R}$ with $Y_{R}=1$ and $\mu_{X}$ variable.
• Figure 5: The correlation of $\mathcal{BR}\left(h\to\mu\tau\right)$ with (a) $v_{R}$, (b) $Y_{R}$ and (c) $\mu_{X}$ in the allowed parameter space.