[en] We present details of our recent calculation of α² corrections to the parapositronium decay into two photons. These corrections are rather small and our final result for the parapositronium lifetime agrees well with the most recent measurement. Implications for orthopositronium decays are briefly discussed. (c) 2000 The American Physical Society

[en] Published in summary form only

[en] The purpose of this study is to give an upper bound for the number of bound states of a short range and spherically symmetrical potential

No abstract available

No abstract available

[en] Confinement of quarks is sometimes taken as some kind of dogma in the contemporary theory of strong interactions - quantum chromodynamics (QCD). As scientists the authors should not be content with that. Rather they should try to formulate what they mean by ''permanent confinement'' more precisely and then see whether the theory has this property or not. In these lectures the author first looks at some possible interpretations of ''confinement'' and their shortcomings and then turn to the most widely used rather pragmatic definition based on the somewhat unphysical notion of infinitely heavy external sources. The author describes what is known - or more precisely what I know - about the problem in this more limited sense and try to bring into focus some aspects that are insufficiently understood

[en] The conditions that must be fulfilled in order to apply the Hypervirial-Perturbative Methods for non-bound states are analysed. (author)

[en] Necessary conditions and sufficient conditions in order to insure one bound state of given (l,m) are obtained for spheroidal potentials using the phase approach: the results are valid for potentials function only of one variable. These results reduce asymptotically to the conditions of Jost-Pais and Calogero in the spherical case and can be useful to detect inversion in the introduction of levels of a given potential

[en] The major contributions of Richard H. Dalitz to hypernuclear physics, since his first paper in 1955 to his last one in 2005 covering a span of 50 years during which he founded and led the theoretical study of hypernuclei, are reviewed from a personal perspective. Topical remarks on the search for quasi-bound K-bar-nuclear states and on kaon condensation are made

[en] Using the adiabatic hyperspherical method, the authors investigate the spectrum of the helium trimer and explore the effects on the spectrum of varying the masses of the helium atoms as well as the interaction strength. They find that the only physical systems that have three-body bound states are ⁴He₃ and ⁴He₂³He. They also determine the range of interaction strengths that result in halo states and examine in detail the special case of Efimov states for both physical and unphysical systems