Poisson-Lie dynamical r-matrices from Dirac reduction

The Dirac reduction technique used previously to obtain solutions of the classical dynamical Yang-Baxter equation on the dual of a Lie algebra is extended to the Poisson-Lie case and is shown to yield naturally certain dynamical r-matrices on the duals of Poisson-Lie groups found by Etingof, Enriquez and Marshall in math.QA/0403283.Comment: 10 pages, v2: minor stylistic changes, v3: corrected eq. (4.3

Bi-Hamiltonian structure of a dynamical system introduced by Braden and Hone

We investigate the finite dimensional dynamical system derived by Braden and Hone in 1996 from the solitons of $A_{n-1}$ affine Toda field theory. This system of evolution equations for an $n\times n$ Hermitian matrix $L$ and a real diagonal matrix $q$ with distinct eigenvalues was interpreted as a special case of the spin Ruijsenaars--Schneider models due to Krichever and Zabrodin. A decade later, L.-C. Li re-derived the model from a general framework built on coboundary dynamical Poisson groupoids. This led to a Hamiltonian description of the gauge invariant content of the model, where the gauge transformations act as conjugations of $L$ by diagonal unitary matrices. Here, we point out that the same dynamics can be interpreted also as a special case of the spin Sutherland systems obtained by reducing the free geodesic motion on symmetric spaces, studied by Pusztai and the author in 2006; the relevant symmetric space being $\mathrm{GL}(n,\mathbb{C})/ \mathrm{U}(n)$. This construction provides an alternative Hamiltonian interpretation of the Braden--Hone dynamics. We prove that the two Poisson brackets are compatible and yield a bi-Hamiltonian description of the standard commuting flows of the model.Comment: 18 pages, references and some explanations added in v

On the Lagrangian Realization of the WZNW Reductions

We develop a phase space path-integral approach for deriving the Lagrangian realization of the models defined by Hamiltonian reduction of the WZNW theory. We illustrate the uses of the approach by applying it to the models of non-Abelian chiral bosons, $W$-algebras and the GKO coset construction, and show that the well-known Sonnenschein's action, the generalized Toda action and the gauged WZNW model are precisely the Lagrangian realizations of those models, respectively.Comment: 15 pages, DIAS-STP-92-09/UdeM-LPN-TH-92-9

The Ruijsenaars self-duality map as a mapping class symplectomorphism

This is a brief review of the main results of our paper arXiv:1101.1759 that contains a complete global treatment of the compactified trigonometric Ruijsenaars-Schneider system by quasi-Hamiltonian reduction. Confirming previous conjectures of Gorsky and collaborators, we have rigorously established the interpretation of the system in terms of flat SU(n) connections on the one-holed torus and demonstrated that its self-duality symplectomorphism represents the natural action of the standard mapping class generator S on the phase space. The pertinent quasi-Hamiltonian reduced phase space turned out to be symplectomorphic to the complex projective space equipped with a multiple of the Fubini-Study symplectic form and two toric moment maps playing the roles of particle-positions and action-variables that are exchanged by the duality map. Open problems and possible directions for future work are also discussed.Comment: Contribution to the proceedings of the workshop `Lie Theory and its Applications in Physics IX' (Varna, June 2011), 13 page