Classically integrable boundary conditions for symmetric-space sigma models

We investigate boundary conditions for the non-linear sigma model on the compact symmetric space G/H. The Poisson brackets and the classical local conserved charges necessary for integrability are preserved by boundary conditions which correspond to involutions which commute with the involution defining H. Applied to SO(3)/SO(2), the non-linear sigma model on S2, these yield the great circles as boundary submanifolds. Applied to G×G/G, they reproduce known results for the principal chiral model.