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Closed-Fermion-Loop Calculations in Chiral Models of Electromagnetic Processes

R. Aviv and R. F. Sawyer

  • Department of Physics, University of California, Santa Barbara, California 93106

Phys. Rev. D 4, 451 – Published 15 July, 1971

DOI: https://doi.org/10.1103/PhysRevD.4.451

Abstract

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 γγpions are unchanged.

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  11. Omitted endnote

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