rayveldkamp said:
) mixes up the two different possible chiralities. This is a result of the famous "tau-theta-puzzle" in QFT. To make a long story short : in QFT all elementary particles are massless because the two chiralities each correspond to a different kind of fundamental "particle-property". I mean, in QFT particles are classified based upon their chirality because a left handed chiral particle does not behave in the same way as a right hand chiral particle. So mass has to be zero (before the spontaneous breakdown of symmetry) because otherwise one particle possesses the TWO chiralities at once (because of the mass-term in the Lagrangian) and thus it is NOT fundamental. So basically photons are always massless because they do not interact with the Higgs-field. They contain a distinct chirality-value and thus not different values for ONE photon. Just look at the V-A-current in the elektroweak-theory : only left handed fermions (or right handed anti-fermions) are involved in weak charged currents.
