The quark loop calculation of the gamma -> 3 pi form factor

TL;DR

This paper calculates the gamma to 3 pi form factor using a quark loop model, providing analytic expressions and numerical results, and compares them with experimental data and other theoretical approaches.

Contribution

It introduces a quark loop calculation for the gamma to 3 pi form factor, extending the analysis to order O(p^8) and comparing with existing models and data.

Findings

Analytic form factor expression up to O(p^8)

Numerical evaluation of the form factor

Comparison with vector meson dominance and chiral perturbation theory

Abstract

The presently experimentally interesting form factor for the anomalous process gamma -> pi^+ pi^0 pi^- is calculated as the quark "box"-amplitude where the intermediate fermion loop is the one of constituent quarks with the pseudoscalar coupling to pions. This also corresponds to the form factor, in the lowest order in pion interactions, of the sigma-model and of the chiral quark model. We give the analytic expression for the form factor in terms of an expansion in the pion momenta up to the order O(p^8) relative to the soft point result, and also perform its exact numerical evaluation. We compare our predictions with those of the vector meson dominance and chiral perturbation theory, as well as with the scarce data available so far.