E. Corrigan et Zm. Sheng, CLASSICAL INTEGRABILITY OF THE O(N) NONLINEAR SIGMA-MODEL ON A HALF-LINE, International journal of modern physics A, 12(16), 1997, pp. 2825-2834
The classical integrability of the O(N) nonlinear sigma model on a hal
f-line is examined, and the existence of an infinity of conserved char
ges in involution is established for the free boundary condition. For
the case N = 3 other possible boundary conditions are considered brief
ly.