1. Theoretical Physics Department, Physics Faculty, National Taras Shevchenko University of Kyiv, Volodymyrs’ka Street 64, 01601 Kyiv, Ukraine
2. Dipartimento SIMAU, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy
3. Department of Physics, University of Warwick, Coventry CV4 7AL, UK