Radiation Decohernce, State Vector Collapse and QED Nonequivalent   Representations
  The state vector evolution in the interaction of initial measured pure state with collective quantum system or the field with a very large number of degrees of freedom N is analysed in a nonperturbative QED formalism. As the example the measurement of the electron final state scattered on nucleus or neutrino is considered.In the nonperturbative field theory the complete manifold of the system states is nonseparable i.e. is described by tensor product of infinitely many independent Hilbert spaces. The interaction of this system with the measured state can result in the final states which belong to different Hilbert spaces which corresponds to different values of some classical observables,i.e. spontaneous symmetry breaking occurs. Interference terms (IT) between such states in the measurement of any Hermitian observable are infinitely small and due to it the final pure states can't be distinguished from the mixed ones, characteristic for the state collapse. The evolution from initial to final system state is nonunitary and become formally irreversible in the limit of infinite time. The electromagnetic (e-m) bremmstrahlung produced in the electron scattering process contain the unrestricted number of soft photons which radiation flux become classic observable. Analoguous processes which occurs in the second kind phase transitions in ferromagnetic and phonon excitations in cristall lattice are considered briefly. 
S.N.Mayburov (Lebedev Inst. of Physics, Moscow, Russia)