Structure of Amplitudes of Neutral-Pion Photoproduction

On the basis of data on polarized-target asymmetry and recoil-proton polarization as well as fixed-$t$ dispersion relations and the low-energy Walker analysis we have constructed the real and imaginary parts of the $\gamma p\to {\pi }^{0}p$ amplitudes at 4 GeV. All imaginary parts are in accord with dual absorptive requirements, and for both real and imaginary helicity-nonflip and -single-flip amplitudes the $t$ structure has many similarities to that of ${\pi }^{-}p\to {\pi }^{0}n$. The satisfaction of duality requirements and finite-energy sum rules by our amplitudes is also discussed in detail.