Some Open Questions

This last and very brief chapter highlights some open problems pertinent to the subject of the book. The main thrust of the book lies in the development of the effective field theory formalism for spontaneously broken symmetry. Accordingly, the list of open questions contains mostly technical issues whose resolution would further extend the validity of the results of the book. Some of the issues, related to the classification of actions of groups of manifolds, are purely mathematical. Others are more directly related to physical applications of the formalism.