QED Lagrangian

  1. Full form of the QED Lagrangian

    Starting from the Lagrangian describing a free Dirac particle
    one obtains a Lagrangian
    which is invariant under a local phase transformation and introduces the interaction between a Dirac particle of charge q with the photon field.

    However, this is not the full QED Lagrangian since a kinetic energy term for the photon field is missing.
    The complete QED Lagrangian is
    The kinetic energy for the photon field is invariant under a local gauge transformation.

  2. Mass of the Photon field
  3. Intermezzo 1: P and C of the photon field
  4. Intermezzo 2: Polarisation vectors of the photon field