Topological defects and θ dependence in QCD.

Abstract

We generalize the large N c Di Vecchia-Veneziano-Witten (VVW) effective chiral Lagrangian to the case of finite N c . The picture of θ dependence in QCD which follows from this Lagrangian is more complicated than suggested by the large N c approach or instanton arguments. Generically, the vacuum energy E vac (θ) is a multi-valued function of θ admitting the existence of metastable states. We discuss applications of the obtained results to the axion physics, baryogenesis and other phenomena which may occur during the QCD epoch in development of the early universe.