From U(1) to U(5): A Bottom-Up Reconstruction of Gauge Unification
We present a unified bottom-up construction of gauge symmetries from U(1) to U(5), demonstrating that each group U(n) ≅ [U(1) × SU(n)]/Z_n generates an additional gauge boson whose physical identity is fixed by anomaly cancellation alone. Starting from U(3), the extra U(1) is uniquely identified as B−L with quark charg...