The current status of the physics of exotic atoms is reviewed. The problem of the anomalous width of the kaonic helium 2p level is analyzed, experimental CPT invariance tests for the antihydrogen are discussed, and results of investigations on the metastability of the antiproton (as well as of π^-, μ^-, K^-, Σ^-, ...) in helium are considered. A comparison is made of the well-known Condo model and the ionic model. In the latter, the ion ( -{p} αee) — a so-called ’ioncule’ — forms after -{p} is stopped in its motion in helium. One of the ioncule’s electrons is weakly bound, resides at one of the Efimov levels, and orbits at ~ 20 a.u. in the dipole field of the neutral ’atomcule’ ( -{p} αe). The lifetime of the ioncule is long (> 10^-5 s) and the antiproton’s vibrational-rotational transition frequencies ω are practically equal to the atomcule value (Δω /ω ~ 10^-5-10^-6 ) — in agreement with laser-spectroscopy data. While the ionic model results on the quenching cross sections of metastable states by impurity atoms and molecules in helium agree well with experiment, the atomcule-based Condo model underrates the cross sections by 3-4 orders of magnitude. The ionic model is also consistent with other experiments. Direct experimental tests of this model are discussed. A new interpretation of E Zavattini’s group’s laser-spectroscopy results on the 2s-2p-splitting in muonic helium is presented.

PACS: 11.30.Er, 25.43+t, 36.30.10-k, 67.40.Kh (all) DOI: 10.1070/PU2001v044n02ABEH000817 URL: https://ufn.ru/en/articles/2001/2/b/ 000170938500002 Citation: Men’shikov L I, Eseev M K "Some problems of the physics of exotic atoms" Phys. Usp. 44 135–171 (2001) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Оригинал: Меньшиков Л И, Есеев М К «Некоторые вопросы физики экзотических атомов» УФН 171 149–185 (2001); DOI: 10.3367/UFNr.0171.200102b.0149