Closed-fermion-loop calculations in chiral models of electromagnetic processes
19717 pages
Published in:
- Phys.Rev.D 4 (1971) 451-457
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Abstract: (APS)
The amplitudes involving two external γ's and an arbitrary number of soft π mesons emitted from a closed nucleon loop have been calculated in a model with a formally conserved (neutral) axial-vector current. The results violate the formal chiral symmetry of the underlying Lagrangian, but in a way that has the following simple group-theoretic interpretation stated in terms of an effective Lagrangian Leff: Instead of finding δLeff=0 under those chiral variations which leave the electromagnetic couplings invariant, we find δLeff to be independent of the chirally transforming fields. If the group-theoretic principle is abstracted from the detailed calculation it leads to predictions for the processes γ+γ→(anoddnumberofpions) which should hold true in a wide class of chiral models. The generalization is given to a quark-loop calculation in a theory invariant under the neutral transformations from SU(3)⊗SU(3)⊗U(1), and the results for γγ→pions are unchanged.- current algebra: effective lagrangians
- symmetry: chiral
- electromagnetic interaction
- photon photon: interaction
- interaction: photon photon
- quark
- symmetry: su(3) x su(3) x u(1)
- pi: photoproduction
- photoproduction: pi
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