The generating functional Z[J] depends on [tex]\phi_{cl}[/tex] trough its dependence on J. At the lowest order in perturbation theory the relation between J(x) and [tex]\phi_{cl}[/tex] is just the classical field equation:(adsbygoogle = window.adsbygoogle || []).push({});

[tex] \left(\frac{\delta L}{\delta \phi}\right)_{\phi=\phi_{cl}} + J(x) = 0 [/tex]

The question is simple: why this expression for the field equation?

Please help me

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Computation of the effective action (Peskin 11.4)

**Physics Forums | Science Articles, Homework Help, Discussion**