Nonperturbative Processes

A few processes are not covered by the discussion so far. These are the ones that depend on the details of hadronic wave functions, and therefore are not strictly calculable perturbatively (although perturbation theory may often provide some guidance). What we have primarily in mind is elastic scattering, diffractive scattering and low-$p_{\perp}$ `minimum-bias' events in hadron-hadron collisions, but one can also find corresponding processes in $\gamma\mathrm{p}$ and $\gamma\gamma$ interactions. The description of these processes is rather differently structured from that of the other ones, as is explained below. Models for `minimum-bias' events are discussed in detail in section , to which we refer for details on this part of the program.