Breaking the Democratic Limit in the Generalized Friedberg-Lee Model: Implications for Neutrino Masses and Mixing

Abstract

We investigate a generalized Friedberg--Lee (FL) framework for neutrino masses, focusing on the singular parameter space at Point D ($\alpha =\beta =-1/3$). At this limit, the neutrino mass matrix exhibits a democratic texture governed by the $S_3$ permutation symmetry. Although theoretically profound, the exact democratic limit is phenomenologically excluded as it predicts a degenerate mass spectrum and a vanishing reactor angle (${\theta }_{13}=0$). To reconcile this high-symmetry limit with experimental observations, we introduce a minimal and systematic perturbation that preserves the Twisted Friedberg--Lee (TFL) symmetry. This mechanism effectively lifts the mass degeneracy and breaks the magic and $\mu$--$\tau$ symmetries in a controlled manner. Our derivation avoids \textit{ad hoc} parameters, establishing a robust framework that yields a realistic inverted mass hierarchy ($m_3=0$), a non-zero ${\theta }_{13}$, and intrinsic CP violation. We demonstrate that the model predicts maximal atmospheric mixing and a significant Dirac CP phase. The obtained numerical ranges for the neutrino masses and the Jarlskog invariant show excellent agreement with global fit data, providing a theoretically motivated foundation for neutrino flavor physics within the TFL scheme.