Current Algebra of Classical Non-Linear Sigma Models
  The current algebra of classical non-linear sigma models on arbitrary Riemannian manifolds is analyzed. It is found that introducing, in addition to the Noether current $j_\mu$ associated with the global symmetry of the theory, a composite scalar field $j$, the algebra closes under Poisson brackets. 
M.Forger, J.Laartz, U.Schaeper