The Quantum Theory of Radiation

4-vector absorption amplitudes angle anticommutes atom Born approximation Bremsstrahlung calculated canonical charge classical theory collision commutation relations components Compton effect Compton scattering consider contribution Coulomb gauge cross-section denote depends effect emission emitted energy loss expectation value external field factor field strengths finite formula free electron free particles frequency given Hamiltonian hermitian high energies integration interaction representation joining points k₁ light quantum line breadth Lorentz condition Lorentz gauge matrix element momenta momentum negative electron negative energy non-relativistic obtain occur operator order of magnitude P. A. M. Dirac pair pair creation photons Phys polarization positive electron positron primary quanta quantization quantum electrodynamics quantum theory radiation field radiative corrections relativistic represents satisfied scattering second quantization second term self-energy subsection test body tion transformation transition probability vacuum vanishes variables vector velocity virtual wave equation wave functions zero