Lessons on e+e? annihilation from simple chain emission models

The dearth of solvable models for e⁺e^? annihilation often reduces one to excessively qualitative considerations, leaving obvious dynamical questions open. We discuss here various aspects of chain-emission models that can be cast into solvable form. In such models the virtual photon decays into a link (a pion, for example) and some state (e.g., an off-shell vector meson) which decays by sequentially shedding further links.Topics include the scaling behavior in such models (including how it is broken near ω = 0), neutral/charged distributions, the effect of internal quantum numbers, and, in a particularly simple version of the model, the two-particle distributions. In particular, we show how a large neutral to charged energy ratio can arise. Finally, we discuss variants on such models arising from possible variety in the links of the chain, (i.e., multichannel effects and the nonlinear effects arising from the branching of a chain into chains.