Exotic atoms - tools to study fundamental interactions and symmetries

Exotic atoms, i.e. atoms where the electron is replaced by another negatively charged particle, are exciting laboratories for studying either the properties of the exotic particle by precision atomic physics techniques, or the interaction of the exotic particle with the nucleons. In this talk I will present two recent examples for both cases.

Laser and microwave spectroscopy of antiprotonic helium yields the most precise value for the antiproton mass and charge and until short time ago also the magnetic moment of the antiproton. The spectroscopy of antihydrogen, the simplest atom consisting purely of antimatter, has the potential of providing the most stringent tests of CPT symmetry in the hadron sector. Progress and plans of the ASACUSA collaboration at the Antiproton Decelerator of CERN will be reviewed.

Light kaonic atoms provide a unique tool to study the kaon-nucelon interaction close to threshold. X-ray measurements of kaonic hydrogen, 4He and 3He by the SIDDHARTA collaboration at DAFNE at Laboratori Nationali di Frascati have provided important data to constrain the strong interaction with strangeness at low energies. A planned experiment on kaonic deuterium would complete the experimental data allowing to extract isospin-dependent scattering lengths.