Negative-norm photon state
= Negative-norm photon state
For a temporal <photon> <wave packet> $|f,0\rangle=\int d^3p\,f(\mathbf p)a_{\mathbf p}^{0\dagger}|0\rangle/(2\pi)^3$, the oscillator <commutator> gives $\langle f,0|f,0\rangle=-\int d^3p\,|f(\mathbf p)|^2/(2\pi)^3<0$ when $f\ne0$. This is the negative direction of the <indefinite Hermitian form>, not the divergent normalization of an unsmeared <momentum eigenstate>. It is excluded by the physical condition in <Gupta-Bleuler quantization>.