Resumen de New geometrical and dynamical techniques for problems in celestial mechanics
Roisin Mary Dempsey Braddell
In this thesis, we study the application of symplectic geometry, regular and singular, to symplectic dynamical systems.We start with a motivating case: the relation between symplectic foliations and global transverse Poincaré sections, showing that meaningful dynamical information can be gleaned by simple observations on the geometry of the phase space - in this case, the existence of a symplectic foliation on a hypersurface of the phase space.
We then go on study dynamical systems of particular importance in geometry - those given by a group action on a manifold. In particular, we consider a singular symplectic manifold (specifically, a manifold equipped with a symplectic form which blows up in a controlled manner on a hypersurface of that manifold, namely, a b-symplectic form) with a group action preserving the geometry and give a b-symplectic slice theorem which provides an equivariant normal form of the b-symplectic form in the neighbourhood of an orbit. Particular examples of b-symplectic group symmetries are then explored: those given by the cotangent lift of group translation on so-called b-Lie groups.
The second part of this thesis focuses on symplectic and b-symplectic dynamical systems coming from celestial mechanics. In particular, the separatrix map of the stable and unstable manifolds of the fixed point at infinity of the planar circular restricted three-body problem is examined and an estimate of the width of the stochastic layer is given - that is the existence of a K.A.M. torus which acts as a boundary to bounded motions is proved. Due to the delicate nature of the problem - namely issues coming from the parabolic nature of the fixed point and exponentially small nature of the splitting, careful control of the errors of the separatrix map is paramount. This is achieved by employing geometric methods, namely, by taking full advantage of generating functions which exist by virtue of the symplectic nature of the system.
Finally, motivated by the important role of symplectic geometry in the systems of celestial mechanics in mind, we give examples of degenerate and singular symplectic structures occurring in systems of celestial mechanics which cannot be equipped with a symplectic form.
