1. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
2. Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, W. Lafayette, IN 47907-2036, USA
3. Institute of Theoretical Physics, Beijing University of Technology, Beijing 100124, China
4. Institute of Theoretical Physics, Jiangxi Normal University, Nanchang 330022, China