We study classical integrable systems based on the Alekseev-Meinrenken dynamical r-matrices corresponding to automorphisms of self-dual Lie algebras, G. We prove that these r-matrices are uniquely characterized by a non-degeneracy property and apply a construction due to Li and Xu to associate spin Calogero type models with them. The equation of motion of any model of this type is found to be a projection of the natural geodesic equation on a Lie group G with Lie algebra G, and its phase space is interpreted as a Hamiltonian reduction of an open submanifold of the cotangent bundle T * G, using the symmetry arising from the adjoint action of G twisted by the underlying automorphism. This shows the integrability of the resulting systems and gives an algorithm to solve them. As illustrative examples we present new models built on the involutive diagram automorphisms of the real split and compact simple Lie algebras, and also explain that many further examples fit in the dynamical r-matrix framework.
IntroductionThe study of integrable many body systems initiated by Calogero [1], Sutherland [2] and Moser [3] is popular since these systems have interesting applications in several branches of theoretical physics and involve fascinating mathematics. See, for example, the reviews in [4,5,6,7]. The generalized Calogero models associated to root systems by Olshanetsky and Perelomov [8], the spin Calogero models due to Gibbons and Hermsen [9], and the Ruijsenaars-Schneider models [10] are also very important. Many approaches were applied to prove the classical integrability of these models. The most general among these are the construction of a Lax representation for the equation of motion and the realization of the system as a 'projection' of some other system that is integrable 'obviously', for example the free geodesic motion on a Lie group or on a symmetric space (see [3,11,12] and the review [4]). The result of Babelon and Viallet [13] linking Liouville integrability to the form of the Poisson brackets (PBs) of the Lax matrix is also relevant for us, since the determination of the r-matrices encoding these PBs in Calogero models led eventually to the questions investigated in this paper.The r-matrices of the A n type spinless Calogero models found in [14,15,16] depend on the coordinates of the particles and are not unitary. They were re-derived by Avan, Babelon and Billey in [17] using Hamiltonian reduction of an auxiliary non-integrable spin extension of the Calogero model. The definition of the non-integrable model relies on a 'quasi-Lax operator', whose PBs (of the type (2.10) below) are encoded by certain unitary dynamical r-matrices that yield the Calogero r-matrices upon reduction. The unitary r-matrices in question were later recognized [18] to be identical to the fundamental solutions of the so-called classical dynamical Yang-Baxter equation (CDYBE) that appeared first in studies of the WZNW conformal field theory [19,20]. Subsequently, the geometric meaning of the CDYBE and the classification of its solutions ...