Anarchic neutrinos from flavor deconstruction: phenomenology of the lepton sector

TL;DR

This work investigates neutrino physics within flavor deconstruction (FD) using an inverse-seesaw (ISS) mechanism, aiming to reconcile hierarchical charged-fermion masses with anarchic light-neutrino mixing. It develops a detailed parameterization linking low-energy neutrino data to a TeV-scale right-handed neutrino sector, yielding three heavy neutral leptons with masses $M_1\sim \Lambda\eta_1\eta_2$, $M_2\sim \Lambda\eta_1$, $M_3\sim \Lambda$, and a light neutrino mass matrix $m_\nu \approx A\mu A^T$ with $A=vY_\nu M_R^{-1}$. The phenomenology is explored through direct HNL searches and LFV observables, showing current bounds push the deconstruction scale to a few TeV (for $y_\nu\sim\mathcal{O}(1)$) and that future $\mu\to e$ experiments will probe most of the viable region with $\Lambda\lesssim 10~\mathrm{TeV}$. Among FD realizations, deconstruction of $SU(2)_L\times U(1)_{B-L}$ or $SU(2)_L\times U(1)_R\times U(1)_{B-L}$ naturally accommodates low-scale dynamics, while $U(1)_R$-only models face LFV tuning challenges. The framework thus provides a predictive connection between neutrino anarchy and TeV-scale flavor dynamics with clear experimental signatures at colliders and LFV experiments.

Abstract

We investigate the neutrino sector in the framework of flavor deconstruction with an inverse-seesaw realization. This setup naturally links the hierarchical charged-fermion masses to the anarchic pattern of light-neutrino mixing. We determine the viable parameter space consistent with oscillation data and study the phenomenology of heavy neutral leptons (HNL) and lepton-flavor-violating (LFV) processes. Current bounds from direct HNL searches and LFV decays constrain the right-handed neutrino scale to a few TeV, while future $μ\to e$ experiments will probe most of the region with $Λ\lesssim 10~\text{TeV}$. Among possible realizations, models deconstructing $\mathrm{SU}(2)_\mathrm{L} \times \mathrm{U}(1)_\mathrm{B-L}$ or $\mathrm{SU}(2)_\mathrm{L} \times \mathrm{U}(1)_\mathrm{R} \times \mathrm{U}(1)_\mathrm{B-L}$ are those allowing the lowest deconstruction scale.

Figures (7)

• Figure 1: Probability distributions of the logarithmic ratios of the eigenvalues $|\mu_1|<|\mu_2|<|\mu_3|$ of an anarchic random matrix $\mu$. The dashed-black lines contain $68\%$ and $95\%$ of the distribution.
• Figure 2: Probability for the parameter $\Delta_i$ to satisfy our anarchic criterion on $\mu$ at $95\%$ CL, assuming Normal Ordering. The three plots refer to different values of the absolute neutrino mass scale: $m_{\nu_1}\in [0.1,1]$ meV (left panel), $m_{\nu_1}\in [1,10]$ meV (central panel), and $m_{\nu_1}\in [10,50]$ meV (right panel).
• Figure 3: Probability for the parameter $\Delta_i$ to satisfy our anarchic criterion on $\mu$ at $95\%$ CL, assuming Inverted Ordering. The two plots refer to different values of the absolute neutrino mass scale: $m_{\nu_3} \in [1,10]$ meV (left panel), and $m_{\nu_1}\in [10,50]$ meV (right panel).
• Figure 4: Plots showing the value of the parameter $K_\ell$ controlling the mixing between the lightest HNL and the SM charged lepton $\ell=e$ (left panel), $\mu$ (central panel) and $\tau$ (right panel), as a function of the $\Delta_i$.
• Figure 5: Prediction of $\mathcal{B}(\mu\rightarrow e\gamma)$ as a function of the NP scale $\Lambda$. The prediction is obtained by varying $\alpha_i$ and $\beta_i$ in the range discussed in Sect. \ref{['subsec:range_of_param']} and setting $\Delta_1=0.45$, $\Delta_2=0.3$, $y_\nu=1$, $\varepsilon_1=0.06$ and $\varepsilon_2=0.04$. The dark-blue (light-blue) band corresponds to the $68\%$ ($95\%$) of the predicted values for a given $\Lambda$. Green lines refer to the present and future experimental limits. The vertical gray band denotes the limit from direct HNL searches at colliders.