|   [1] Witten E. Non-abelian bosonization in two-dimensions. Commun Math Phys, 1984, 92: 455–472 
 
[2] Nappi C, Witten E. Wess-Zumino-Witten model based on a nonsemisimple group. Phys Rev Lett, 1993, 23: 3751–3753 
 
[3] Kiritsis E, Kounnas C. String propagation in gravitational wave backgrounds. Phys Lett B, 1994, 594: 368–374 
 
[4] Cheung Y, Freidel L, Savvidy K. Strings in gravimagnetic fields. J High Energy Phys, 2004, 054: 1–48 
 
[5] D´Appollonio G, Quella T. The abelian cosets of the Heisenberg group. J High Energy Phys, 2007, 045 
[6] D´Appollonio G, Quella T. The diagonal cosets of the Heisenberg group. J High Energy Phys, 2008, 060 
 
[7] D´Appollonio G, Kiritsis E. String interactions in gravitational wave backgrounds. Nucl Phys B, 2003, 674: 80–170 
 
[8] Bao Y X, Jiang C P, Pei Y F. Representations of affine Nappi-Witten algebras[D]. Shanghai: Shanghai University, 2008 
 
[9] Wang S. Automorphism groups of rank one lattice vertex operator superalgebras. Acta Math Sci, 2012, 32A(2): 290–296 
 
[10] Lian B. On the classification of simple vertex operator algebras. Commun Math Phys, 1994, 163: 307–357 
 
[11] Lepowsky J, Li H. Introduction to Vertex Operator Algebras and Their Representations. Progress in Math, 227. Boston: Birkhäuser, 2003 
 
[12] Frenkel I, Zhu Y. Vertex operator algebras associated to representations of affine and Virasoro algebras. Duke Math J, 1992, 66: 123–168 
 
[13] Frenkel I, Lepowsky J, Meurman A. Vertex Operator Algebras and the Monster. Pure and Appl Math, 134. Boston: Academic Press, 1988  |