Protonium and other exotic --p - atoms

This chapter discusses the spectroscopy of protonium using the Low-Energy Antiproton Ring (LEAR). Topics covered include electromagnetic and relativistic effects, strong interaction effects in protonium, exotic phenomena in protonium (baryonium, Van der Waals forces, axions and other exoticons), and antiprotonnucleus exotic atoms. It is demonstrated that the electromagnetic effects and relativistic correction should be estimated very accurately; there is a delicate interplay of the nuclear and coulombic forces in protonium; important many-body and off-shell effects can arise in heavier nuclei when deriving the -p-nucleus optical potential from the elementary -p-nucleon interaction; and there is the possibility of new phenomena, such as long-range hadronic Van-der-Waals forces or the exchange of very light particles like axions