... numbers of particles of various types. These are called ‘in’ and ‘out’, |α, in and |β, out,whereα and β denote sets of quantumnumbers characterizing momenta, spin z-components and types of particle ... fields as an infinite number of degrees of freedom limit of systems of coupled oscillatorsIn order to approach the consideration of systems with an infinite number of degrees of freedom (quantum fields) ... Bogoliubov and Shirkov (1959), Schweber (1961), Bjorken and Drell (1965), Itzykson and Zuber (1980), Chaichian and Nelipa (1984), Greiner and Reinhardt (1989), Peskin and Schroeder(1995) and Weinberg...