Fermion number
= Fermion number
{title2=$Q=\int d^3x\,:\!\psi^\dagger\psi\!:$}
For a <Dirac field> with a <global phase symmetry>, <fermion number> is the vacuum-subtracted charge of the <Dirac current>. In a mode expansion it counts particles minus antiparticles, with the overall sign fixed by the chosen generator convention. It is distinct from the total number of fermionic excitations and from <fermion parity>, which can survive even when interactions violate the continuous charge.