  We present a unified model without the need for an ad hoc Standard Model
hypothesis; we explain why there are three generations of charged and neutral
leptons, why neutrinos have a vanishingly small mass, and why flavor-mixing
emerges and mass oscillations occur. We show that the sedenion algebra contains
three types of non-associative octonion algebra, with each corresponding to a
generation of leptons. By incorporating extra degrees of freedom, the
generalized higher dimensional Dirac equation accounts for the internal
structural dynamics. This study sheds light on the intrinsic physical
properties of three generations of charged leptons and neutrinos and their
distinctive spacetime structures.
