A NEW DUAL SYMMETRY STRUCTURE OF THE KP HIERARCHY

A new infinite set of commuting additional (''ghost'') symmetries is p roposed for the KP-type integrable hierarchy. These symmetries allow f or a Lax representation in which they are realized as standard isospec tral flows. This gives rise to a new double-KP hierarchy embedding ''g host'' and original KP-type Lax hierarchies connected to each other vi a a ''duality'' mapping exchanging the isospectral and ''ghost'' ''tim es''. A new representation of the 2D Toda lattice hierarchy as a speci al Darboux-Backlund orbit of the double-KP hierarchy is found and para metrized entirely in terms of (adjoint) eigenfunctions of the original KP subsystem. (C) 1998 Published by Elsevier Science B.V.