= Source
{disambiguate=quantum field theory}
{title2=$J(x)$}
= External source
{synonym}
= Source
{synonym}
An external <source> is a prescribed field coupled to a dynamical field or operator in the action, for example $S_J=S_0+\int J_i(x)\phi_i(x)\,d^dx$. Functional derivatives of the <generating functional> with respect to $J$ insert the corresponding fields into correlation functions. The source is varied to generate these insertions, rather than integrated over as a dynamical degree of freedom. Transforming it in the appropriate representation maintains an invariant source coupling when deriving a <Ward identity>.
Back to article page
