Question about
this. The typical way to go is to note that there is this ambiguity due to the $\phi^\ast\overset{\leftrightarrow}{\partial_0}\phi$ ordering problem and then remove it by postulating the vacuum bears no charge. It turns out this is the same as normal ordering.I wonder what would be the ordering choice to be made on $\phi^\ast\overset{\leftrightarrow}{\partial}_0\phi$ to get it normal ordered directly