= One-particle state
{title2=$a^\dagger(f)|0\rangle$}
A <one-particle state> belongs to the one-excitation sector of a <Fock space>. In a momentum basis with $[a_{\mathbf p},a_{\mathbf q}^\dagger]=(2\pi)^3\delta^3(\mathbf p-\mathbf q)$, the wavepacket $\int d^3p\,f(\mathbf p)a_{\mathbf p}^\dagger|0\rangle/(2\pi)^3$ has norm squared $\int d^3p\,|f(\mathbf p)|^2/(2\pi)^3$. Sharp-momentum states have distributional rather than unit normalization; factors of $\sqrt{2E_{\mathbf p}}$ convert to <relativistic normalization of a one-particle state>.
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