Two physical polarizations of a photon ($N_{\mathrm{phys}}=2$)

Two first-class constraints in Maxwell theory remove four phase-space variables from the eight variables of a four-component potential and its momenta. The remaining four phase-space variables form two canonical pairs. In radiation gauge these are transverse polarization modes; circular combinations have helicity $+1$ and $-1$. Auxiliary covariant-gauge components do not add physical photon states.