作者机构:[1]Department of Physics, Institute of Theoretical Physics, Beijing Normal University, Beijing 100875, China
相关基金:Project supported by the National Natural Science Foundation of China (Grant Nos. 10773002 and 10875012) and the National Basic Research Program of China (Grant No. 2003CB716302).Acknowledgments We would like to give great thanks for the helpful discussions with Prof. Zheng Zhao.