[1] Nanjing Normal Univ, Dept Phys, Nanjing 210023, Jiangsu, Peoples R China
[2] Nanjing Normal Univ, Inst Theoret Phys, Nanjing 210023, Jiangsu, Peoples R China
[3] Chinese Acad Sci, Inst High Energy Phys, Key Lab Particle Astrophys, Beijing 100049, Peoples R China
[4] Chinese Acad Sci, Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[5] Univ Tubingen, Inst Astron & Astrophys, Sand 1, D-72076 Tubingen, Germany