VALLEY INSTANTON IN THE GAUGE-HIGGS SYSTEM

The instanton configuration in the SU(2)-gauge system with a Higgs dou blet is constructed by using the new valley method. This method define s the configuration by an extension of the field equation and allows t he exact conversion of the quasi-zero eigenmode to a collective coordi nate. It does not require ad hoc constraints used in the current const rained instanton method and provides a better mathematical formalism t han the constrained instanton method. The resulting instanton, which w e call ''valley instanton'', is shown to have the desirable behaviors. The result of the numerical investigation is also presented.