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? [tex] \left \langle \varphi(x) \varphi(y) \right\rangle= \int D\varphi D A \varphi(x) \varphi(y) \exp \left( -S_E [\varphi,A] \right), [/tex] where [itex] S_E [/itex] is an Euclidean action, [itex] \varphi [/itex] bosonic field and [itex] A [/itex] 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 [itex] S_E [/itex], 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. Thank you in advance!