= QED mass counterterm coefficients and the bare mass
{c}
{title2=$\delta m_L=Z_2m_0-m$}
With renormalized <Dirac fields>, the coefficient of $-\bar\psi\psi$ in the <counterterm Lagrangian> is $\delta m_L=Z_2m_0-m$, whereas the bare-parameter shift is $m_0-m=\delta m_L-m\delta Z_2$ at first order. In <Feynman gauge> and $d=4-\epsilon$, <QED> has $\delta Z_2=-e^2/(8\pi^2\epsilon)$ and $\delta m_L=-4me^2/(8\pi^2\epsilon)$. Their difference gives $m_0-m=-3me^2/(8\pi^2\epsilon)$. Defining the insertion and the <mass> coefficient before quoting its sign avoids confusing these two <counterterms>.
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