[1] Joint Inst Nucl Res, Dubna, Russia
[2] Inst Adv Study, Princeton, NJ 08540 USA
[3] Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin, Italy
[4] Univ Turin, Dipartimento Fis Teor, I-10125 Turin, Italy
[5] Univ Vienna, Inst Theoret Phys, A-1090 Vienna, Austria