1. Nordita KTH Royal Institute of Technology and Stockholm University Roslagstullsbacken 23 SE‐106 91 Stockholm Sweden
2. Institut für Mathematische Physik Technische Universität Braunschweig Mendelssohnstraße 3 38106 Braunschweig Germany
3. Faculty of Physics Kyiv National Taras Shevchenko University 64/13 Volodymyrska st. 01601 Kyiv Ukraine
4. Bogolyubov Institute for Theoretical Physics 03680 Kyiv Ukraine