[1] Sichuan Univ, Coll Phys, Ctr Theoret Phys, Chengdu 610064, Peoples R China
[2] Durban Univ Technol, Inst Syst Sci, ZA-4000 Durban, South Africa
[3] Univ Austral Chile, Inst Ciencias Fis & Matemat, Valdivia 5090000, Chile
[4] Univ Athens, Nucl & Particle Phys Sect, Dept Phys, Athens 15771, Greece