Antiproton-hydrogen annihilation at subkelvin temperatures

The main properties of the interaction of ultralow-energy antiprotons (E less than or equal to 10(-6) a.u.) with atomic hydrogen are established. They include the elastic and inelastic cross sections and protonium (Pn) formation spectrum. The inverse;Auger process (Pn+e-->H+(p) over bar) is taken into account in the;framework of a unitary coupled-channel model. The annihilation cross section is found to be several times smaller than the predictions made by the black sphere absorption models. A family of pH near-threshold metastable states is predicted. The dependence of protonium formation probability on the position of such near-threshold S-matrix singularities is analyzed. An estimation for the <H(H)over bar> annihilation cross section is obtained.