ANTIHYDROGEN AT SUB-KELVIN TEMPERATURES

We discuss the behavior of magnetically trapped antihydrogen (HBAR) at temperatures relevant for gravity and spectroscopy experiments (well below 1 K) and the possibilities of attaining these temperatures. Two possible options are considered. In the discussion of the first one, i.e. HBAR as admixture in cold H gas, we develop the quantum-mechanical theory of HBAR-H (and also pBAR-H) elastic and rearrangement collisions at ultra-low (sub-Kelvin) energies, when s-wave scattering in the incoming channel dominates. The rate constant of rearrangement leading to HBAR decay turns out to be large, which makes the possibilities for HBAR collisional cooling in H gas and HBAR-H coexistence rather limited. As we show, the most promising is the other option, i.e. HBAR atoms in the collisionless regime. For this regime the possibility of one-dimensional adiabatic cooling of HBAR is demonstrated by using the example of the Ioffe trap. This phenomenon, interesting from the fundamental point of view, offers the opportunity to cool HBAR below 1 mK.