# Instanton contribution to two point function

1. Dec 19, 2011

### physengineer

Hello,

I would appreciate it if anyone could help me with this problem: can there be any instantonic contribution to the following generic two-points function?

$$\left \langle \varphi(x) \varphi(y) \right\rangle= \int D\varphi D A \varphi(x) \varphi(y) \exp \left( -S_E [\varphi,A] \right),$$
where $S_E$ is an Euclidean action, $\varphi$ bosonic field and $A$ is the gauge field.

I am not sure even if my question makes any sense. I have seen people calculate instability of the vacuum of the action $S_E$, which was just from the partition function. I do not know if I have to be careful about instantons when I calcualte a two-points function or not.