Partition Function (quantum Field Theory) - Uses

Uses

The prototypical use of the partition function is to obtain Feynman amplitudes by differentiating with respect to the auxiliary function (sometimes called the current) J. Thus, for example:

\langle G(x_1,x_2)\rangle = \left. -\frac{\delta}{\delta J(x_1)} \frac{\delta}{\delta J(x_2)} \log Z \right|_{J=0}

is the Green's function, propagator or correlation function for the field between points and in space.

Read more about this topic:  Partition Function (quantum Field Theory)