1. Department of Physics, Keio University, Kanagawa 223-8521, Japan
2. Institut de Mathématiques de Bourgogne, Université Bourgogne Franche-Comté, 21078 Dijon, France
3. Leinweber Center for Theoretical Physics, University of Michigan, Ann Arbor, MI 48109, USA
4. Riemann Center for Geometry and Physics, Leibniz University Hannover, D-30167, Germany
5. Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China