[1] Univ Padua, Dipartimento Fis, Ist Nazl Fis Nucl, Sez Padova, I-35131 Padua, Italy
[2] Tomsk State Pedagog Univ, Dept Theoret Phys, Tomsk 634041, Russia
[3] Joint Inst Nucl Res, Bogoliubov Lab Theoret Phys, Dubna 141980, Russia
[4] Georgian Acad Sci, Inst Phys, GE-380077 Tbilisi, Georgia