For a Lie groupoid G with Lie algebroid A, we realize the symplectic leaves of the Lie-Poisson structure on A * as orbits of the affine coadjoint action of the Lie groupoid J G ⋉ T * M on A * , which coincide with the groupoid orbits of the symplectic groupoid T * G over A * . It is also shown that there is a fiber bundle structure on each symplectic leaf. In the case of gauge groupoids, a symplectic leaf is the universal phase space for a classical particle in a Yang-Mills field.
Coadjoint representation of Lie groupoidsFor a Lie groupoid, there is no natural way to define an ordinary adjoint representation. One approach is to construct a representation up to homotopy of the Lie groupoid G on the normal complex A ⊖ T M [6], where A → M is the Lie algebroid of G. See also [1] for more detailed discussion. On the other hand, unlike the Lie groupoid G itself, the first jet groupoid J G has a natural representation on the normal complex A ⊖ T M [6,4]. We refer to [12] for the general theory of Lie groupoids and algebroids.Here we shall first recall the definitions of adjoint and coadjoint representations given by the second idea. Then we discuss the mechanical properties of the coadjoint representation.Given a Lie groupoid G ⇒ M and a surjective smooth map J : P → M , a left action of G on P along the map J, called the moment map, is a smooth map G × M P → P, (g, p) → g · p satisfying the following:where G × M P = {(g, p)|r(g) = J(p)}. Then P is called a left G-space. A representation of a groupoid G ⇒ M is a vector bundle E over M with a linear action of G on E, i.e. for each arrow g : x → y, the induced map g· : E x → E y on the fibers is a linear isomorphism.Let G be a Lie groupoid with Lie algebroid A. A bisection of G is a splitting b : M → G of the source map r with the property that φ b := l • b : M → M is a diffeomorphism. The bisections of G form a group Bis(G) with the multiplication and inverse given by