Narrow Results

The pion optical potential generated by the hypothetical πNN-coupled NN-decoupled dibaryon resonance d′(2065) is calculated to the lowest order in nuclear matter density. The contribution to the pion optical potential is found to be within the empirical errors, so the d′(2065) existence currently does not contradict to the observed properties of the π^--nucleus bound states. Future progress in the pionic X-ray spectroscopy can reveal contributions of πNN resonances to energy levels and widths of the pionic atoms.

Medium-modification of hadronic interactions is defined as the differences between hadron-hadron interaction in the nuclear medium and the corresponding interaction in free space. Deeply penetrating hadrons provide such information and we discuss here pionic atoms and scattering by nuclei of 21.5 MeV pions. Brief mention is made also of the interaction of 500-700 MeV/c K⁺ with nuclei.

Predictions of the existence of well-defined deeply bound pionic atom states for heavy nuclei and the eventual observation of such states by the (d,³He) reaction have revived interest in the pion-nucleus interaction at threshold and in its relation to the corresponding pion-nucleon interaction. Explanation of the 'anomalous' s-wave repulsion in terms of partial restoration of chiral symmetry and/or in terms of energy-dependence effects have been tested in global fits to pionic atom data and in a recent dedicated elastic scattering experiment. The role of neutron density distributions in this context is discussed in detail for the first time.

In recent years a large number of new states in the charm sector was discovered above the first inelastic threshold that not at all match to the predictions of the quark model, which on the other hand was extremely successful below that threshold. Since most of those states are located close to a two–hadron threshold, many authors proposed a molecular nature for them. In this talk we will collect the evidences and discuss how the picture can be tested further. In addition, if hadron loops induce non-perturbative effects above the inelastic threshold, one should also expect them to have some impact on the properties of standard charmonia. In the last part of this write-up an effective field theory is introduced that allows one to investigate this issue systematically.

The results of laser spectroscopy experiments of antiprotonic helium atoms carried out at the Antiproton Decelerator of CERN, and pionic helium atoms measured at the 590MeV ring cyclotron facility of the Paul Scherrer Institute are reviewed. The former experiment determined the antiproton-to-electron mass ratio as $M_{\overline{p}}/m_e=1836.1526734(15)$. In the latter, a resonant transition $(n,\ell )=(17,16)\to (17,15)$ of pionic helium at a frequency of $\nu \approx 183760$GHz was detected. Some future perspectives are briefly described.