1. Theoretical Physics Division, Chern Institute of Mathematics, Nankai University, Tianjin, 300071, P. R. China
2. Department of Physics, Tianjin University, Tianjin 300072, P. R. China
3. School of Finance, Capital University of Economics and Business, Beijing 100070, P. R. China
4. Institute of Quantitative Finance and Risk Management, Capital University of Economics and Business, Beijing 100070, P. R. China