Primary momentum constraint of the electromagnetic potential
= Primary momentum constraint of the electromagnetic potential
{title2=$\Pi^0=0$}
The Maxwell <Lagrangian density> contains no time derivative of $A_0$, so its <canonical momentum> vanishes. The condition is a <first-class constraint>. Its time preservation yields the <Gauss law constraint in gauge theory>; $A_0$ acts as the corresponding multiplier in the <Hamiltonian>.