Quantization of free scalar fields scalar field f require (i) Lorentzian invariance (ii) invariance under f → -f (iii) at most quadratic in f Lagrangian density = Lagrangian equation of motin Klein Gordon equation canonical conjugate momentum canonical commutator relation =quantization condition time-development of F Hamiltonian density
Klein Gordon equation solution put negative energy! general solution vacuum state Fock space Hamiltonian take f as an operator : operator creation operator annihilation operator
general solution vacuum state Fock space 補助条件 annihilation operator creation operator gauge invariant Lagrangian density complex scalar gauge transformation for matter field covariant derivative