= Covariant photon Fock space
The covariant free-photon oscillator construction uses four <polarization vectors> and $[a^\lambda,a^{\lambda'\dagger}]=-\eta^{\lambda\lambda'}$. Starting from a positive <Fock vacuum>, it induces an <indefinite Hermitian form> on the multiparticle state space: the temporal oscillator has negative norm while the three spatial oscillators have positive norm. It is therefore not the physical positive <Hilbert space>. The <Gupta-Bleuler null-state quotient> selects a positive physical space with two transverse photon polarizations. Continuum <momentum> oscillators and their states are understood after smearing or finite-volume regularization.
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