Topological susceptibility and contact term in QCD: A toy model

We study a number of different ingredients related to theta dependence, the nondispersive contribution in topological susceptibility with the wrong sign, topological sectors in gauge theories, and related subjects using a simple deformed QCD. This model is a weakly coupled gauge theory, which however has all the relevant essential elements allowing us to study difficult and nontrivial questions which are known to be present in real strongly coupled QCD. Essentially, we want to test the ideas related to the U(1)(A) problem in a theoretically controllable manner using the deformed QCD as a toy model. One can explicitly see microscopically how the crucial elements work.