GEOMETRY, DYNAMICS AND SPECTRAL ANALYSIS ON MANIFOLDS The Pestov Identity on Frame Bundles and Eigenvalue Asymptotics on Graph-like Manifolds

This dissertation is made up of two independent parts. In Part I we consider the Pestov Identity, an identity stated for smooth functions on the tangent bundle of a manifold and linking the Riemannian curvature tensor to the generators of the geodesic flow, and we lift it to the bundle of k-tuples of tangent vectors over a compact manifold M of dimension n. We also derive an integrated version over the bundle of orthonormal k-frames of M as well as a restriction to smooth functions on such a bundle. Finally, we present a dynamical application for the parallel transport of the Grassmannian of oriented k-planes of M. In Part II we consider a family of compact and connected n-dimensional manifolds, called graph-like manifold, shrinking to a metric graph in the appropriate limit. We describe the asymptotic behaviour of the eigenvalues of the Hodge Laplacian acting on differential forms on those manifolds in the appropriate limit. As an application, we produce manifolds and families of manifolds with arbitrarily large spectral gaps in the spectrum of the Hodge Laplacian

The reflection principle in the control problem of the heat equation

We consider the control problem for the generalized heat equation for a Schr\"odinger operator on a domain with a reflection symmetry with respect to a hyperplane. We show that if this system is null-controllable, then so is the system on its respective parts. Moreover, we show that the corresponding control cost does not exceed the one on the whole domain.Comment: 19 pages, 3 figure

Geometric conditions for the null-controllability of hypoelliptic quadratic parabolic equations with moving control supports

International audienceWe study the null-controllability of some hypoelliptic quadratic parabolic equations posed on the whole Euclidean space with moving control supports, and provide necessary or sufficient geometric conditions on the moving control supports to ensure null-controllability. The first class of equations is the one associated to non-autonomous Ornstein-Uhlenbeck operators satisfying a generalized Kalman rank condition. In particular, when the moving control supports comply with the flow associated to the transport part of the Ornstein-Uhlenbeck operators, a necessary and sufficient condition for null-controllability on the moving control supports is established. The second class of equations is the class of accretive non-selfadjoint quadratic operators with zero singular spaces for which some sufficient geometric conditions on the moving control supports are also given to ensure null-controllability