Spin-Exchange in Hydrogen-Antihydrogen Collisions

We consider the spin-exchange in ultracold collisions of hydrogen ($H$) and antihydrogen ($\bar{H}$) atoms. The cross sections for transitions between various hyperfine states are calculated. We show that the process of spin exchange in $\bar{H}-H$ collisions is basically driven by the strong force between proton and antiproton, that spin-exchange cross-sections are proportional to the difference of singlet and triplet strong force S-wave scattering lengths, while the strong force effects are enhanced about $10^9$ times due to long range atomic forces. We show that any difference in hyperfine structure of $H$ and $\bar{H}$ (CPT violation) manifests itself in radical change of spin-exchange cross-sections energy behavior.