Gauge kinetic term ($-\frac{1}{4}{F}_{\mu \nu }{F}^{\mu \nu }$)

The field-strength quadratic term supplies gauge-field dynamics. In the canonical Abelian normalization it is $-F_{\mu \nu }{F}^{\mu \nu }/4$; a non-Abelian theory includes the invariant sum or trace over internal indices. A vector mass inferred from a scalar kinetic term is physical only after specifying this normalization.