# Bound states and extensive field configurations

1. What are extensive field configurations in QFT (instantons, monopoles etc.)?

2. What is the difference in description of their contribution in path integral value or in $n$-point operator functions from description of contribution of bounded states like pion?

They are both nonperturbative effects, but I don't understand how extensive field configurations appear, especially in operator formalism in QFT.

• Comment to the question (v3): Did you mean extended rather than extensive? – Qmechanic Oct 8 '14 at 17:48
• @Qmechanic : it seems to me that these two words mean the same thing – user8817 Oct 8 '14 at 18:31
• I do not understand your question. Are you asking what instantons are, or why one might call them "extended field configurations"? Also, why do you believe the description is different for PI and OF pictures? The (4D, Yang-Mills) instanton is, in both, simply a self-dual gauge field. – ACuriousMind Oct 8 '14 at 22:37
• @ACuriousMind : "...Are you asking what instantons are, or why one might call them "extended field configurations"?.." - the second one. "...The (4D, Yang-Mills) instanton is, in both, simply a self-dual gauge field...", - and what about, for example, domain walls? – user8817 Oct 9 '14 at 3:35