1. Theoretical Physics and Astronomy Department, The Herzen University, 48 Moika, St. Petersburg 191186, Russia
2. A. Friedmann Laboratory for Theoretical Physics, St. Petersburg 191186, Russia
3. Institute of Problems in Mechanical Engineering of Russian Academy of Sciences, 61 Bolshoy, V.O., St. Petersburg 199178, Russia
4. N.I. Lobachevsky Institute of Mathematics and Mechanics, Kazan Federal University, Kazan 420008, Russia