Functional Jacobian
= Functional Jacobian
{title2=$J[\phi]=\det[\delta F(x)/\delta\phi(y)]$}
For a change of field variables $\phi\mapsto F[\phi]$, the functional Jacobian is the <functional determinant> of the linearized change. At a finite regulator it is an ordinary <Jacobian determinant> on the finitely many field coordinates; the continuum expression denotes the regulated limit. It changes the <functional integral> measure and can depend on the background field. The <Faddeev-Popov determinant> is the example obtained by replacing the integration coordinate along a <gauge orbit> by a chosen <gauge fixing> condition.