Coherent State Description of Extended Objects: Stability and Orthonormality Problems

A convenient method of describing an extended object 111 quantum field theory, wh1ch '" regarded as a hadron, is presented. We describe the extended object by a coherent state and treat it on the basis of a variational approximation. The stability and orthogonality problems which are crucial in any attempt to render a physical significance to such a coherent state are investigated. From the stability condition, it lS shown that only the models which induce the spontaneous breakdown of symmetry have a stable coherent state. We also show that several topological conservation laws can be understood as a reflection of the orthogo nality properties of the Hilbert space. As simple examples, we discuss a self-coupled neutral scalar model, a charged scalar model, the Higgs model and the 0 (3) iso-triplet scalar model.