1. Bogolyubov Institute for Theoretical Physics (BITP), Ukrainian National Academy of Sciences, 14-b Metrologicheskaya Str., 03680 Kiev, Ukraine
2. Physikalisches Institut, Heidelberg University, Im Neuenheimer Feld 226, 69120 Heidelberg, Germany
3. Uzhgorod National University, 14 Universytets’ka Str., 88000 Uzhgorod, Ukraine