Crossover and Polarization Phenomena in High-Energy Scattering. Cuts, Conspiracies, and Secondary Regge Poles

The usual interpretation, in Regge-pole models, of the change in signs of the cross section differences $\frac{d\sigma \left(\overline{A}B\right)}{\mathrm{dt}}-\frac{d\sigma \mathrm{}\left(\mathrm{AB}\right)\mathrm{}}{\mathrm{dt}}$ at $t\sim -0.15\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ observed in elastic $\pi N$, $\mathrm{KN}$, and $\mathrm{NN}$ scattering is inconsistent with recent data on the reaction $\gamma p\to {\pi }^{0}p$. It is pointed out that this contradiction is direct evidence for the existence of contributions to the high-energy scattering amplitudes in addition to those of the leading Regge poles. Alternative explanations of the crossover phenomena which avoid the foregoing difficulty are proposed, and their implications are discussed.