# Tag Info

The calculation you are referring to is for the current induced by a fixed background electromagnetic field in two-dimensional massless QED. Having a background field means quantising the usual fermionic action $$\bar{\psi}(iD\!\!\!/)\psi$$ with $D_\mu=\partial_\mu + i e A_\mu(x)+i e B_\mu(x)$, where $A_{\mu}(x)$ is a fixed, classical gauge field ...