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1. Unitarity

   Linked via "neutrino species"

   The concept of unitarity is crucial in describing flavor transformations, particularly in the context of neutrino oscillations. The matrix describing the mixing between neutrino flavor states ($\nu\alpha$) and mass states ($\nuj$) is the Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix, denoted $U_{\text{PMNS}}$ [4].
   The PMNS matrix is mandated to be a complex unitary matrix ($U^\dagger U = I$). This unitarity …