Quantum field theories around a large-Z nucleus: Metastable states in supercritical phase

We show that new metastable charge-neutral excitations exist in the supercritical phase of QED around a hypothetical large-Z nucleus. They are the vibration modes of the electron cloud induced around the external charge, and therefore do not have their counterpart in the normal phase. To uncover their properties we utilize our bosonized formulation of QED with proper care of renormal-ordering. In this framework the states can be described as small fluctuations on the solitonic ground state. Their energy levels and the widths are estimated by using the WKB approximation. Some of them are found to be very narrow, of the order of 1-10 keV, and have energies around ≅ 1.6 MeV. The nature of the states is clarified and their quantum numbers are determined: JPC=O+- and 1++. Possible relevance of these states to the anomalous peak structure found in heavy ion collision experiments is briefly discussed and a new coincidence experiment is proposed to test this picture. (orig.)