Bordemann M., Forger M., Laartz J., Schaeper U.
{The Lie-Poisson Structure of Integrable Classical Non-Linear Sigma
 Models
(108K, LaTex)

ABSTRACT.  The canonical structure of classical non-linear sigma models on Riemannian
symmetric spaces, which constitute the most general class of classical
non-linear sigma models known to be integrable, is shown to be governed by
a fundamental Poisson bracket relation that fits into the $r$-$s$-matrix
formalism for non-ultralocal integrable models first discussed by Maillet.
The matrices $r$ and $s$ are computed explicitly and, being field dependent,
satisfy fundamental Poisson bracket relations of their own, which can be
expressed in terms of a new numerical matrix~$c$. It is proposed that
all these Poisson brackets taken together are representation conditions
for a new kind of algebra which, for this class of models, replaces the
classical Yang-Baxter algebra governing the canonical structure of ultralocal
models. The Poisson brackets for the transition matrices are also computed,
and the notorious regularization problem associated with the definition of
the Poisson brackets for the monodromy matrices is discussed.