Solution
= Solution
In four dimensions, $[\psi]=3/2$, $[A_\mu]=1$, and $[F_{\mu\nu}]=2$. The minimal-coupling operator $\bar\psi\gamma^\mu A_\mu\psi$ has dimension four, so $[e]=0$ and $e$ is a <marginal coupling>. The <Pauli term> $\bar\psi[\gamma^\mu,\gamma^\nu]F_{\mu\nu}\psi$ has dimension five, so $[\lambda]=-1$ and $\lambda$ is an <irrelevant coupling> by <power counting in quantum field theory>.