We study a method to induce resonant transitions between antihydrogen quantum states above a material surface in the gravitational field of the Earth. The method consists in applying a gradient of magnetic field which is temporally oscillating with t
he frequency equal to a frequency of a transition between gravitational states of antihydrogen. Corresponding resonant change in a spatial density of antihydrogen atoms can be measured as a function of the frequency of applied field. We estimate an accuracy of measuring antihydrogen gravitational states spacing and show how a value of the gravitational mass of the antihydrogen atom can be deduced from such a measurement.
Hadron electromagnetic form factor in the time-like region at the boundary of the physical region is considered. The energy behavior of the form factor is shown to be determined by the strong hadron-antihadron interaction. Imaginary parts of the scat
tering lengths for $pbar{p}$, $Lambdabar{Lambda}$, $Lambdabar{Sigma}^0 (bar{Lambda}{Sigma}^0)$ and ${Sigma}^0bar{Sigma}^0$ are estimated. Developed approach enables us to estimate imaginary part of the scattering volume from $D^*bar{D^*}$ experimental data. The form factor energy behavior away from the threshold is obtained within a semiphenomenological model of hadron-antihadron interaction.
