Electroweak gauge symmetry ($SU(2{)}_L\times U(1{)}_Y$)

The local gauge structure of the Standard Model electroweak sector. Left-chiral fermions form weak-isospin doublets and hypercharge assignments determine the electromagnetic generator $Q=T_3+Y$ in one common normalization. A chosen Higgs field vacuum leaves the electromagnetic subgroup manifest. Gauge transformations remain a redundancy of the description; physical vector masses are gauge-invariant observables.