Heavy Pion, Modified Partially Conserved Axial-Vector Current Hypothesis, andπ0→2γ: Classification of New Models, Including Gauge Models

The gauge model of hadrons strongly suggests a heavy pion. Motivated by this, we classify and discuss general chiral-like models, including a heavy pion. Workable models are discussed with respect to a number of popular theoretical ideas. Particular attention is paid to such topics as ${\pi }^0\to 2\gamma$, the anomaly-free partially conserved axial-vector current relations of the gauge model, and Lagrangian realization of Drell's recent dispersion model.