In this talk we will discuss a new geodesic beam approach to understanding eigenfunction concentration. We characterize the features that cause an eigenfunction to saturate the standard supremum bounds in terms of the distribution of $L^{2}$ mass along geodesic tubes emanating from a point. We also show that the phenomena behind extreme supremum norm growth is identical to that underlying extreme growth of eigenfunctions when averaged along submanifolds. Using the description of concentration, we obtain quantitative improvements on the known bounds in a wide variety of settings.[-]

Geodesic flow on ellipsoids is one of the most celebrated classical integrable systems considered by Jacobi in 1837.
Moser revisited this problem in 1978 revealing the link with the modern theory of solitons.
Surprisingly a similar question for hyperboloids did not get much attention, although the dynamics in this case is very different.
I will explain how to use the remarkable results of Moser and Knoerrer on the relations between Jacobi problem and integrable Neumann system on sphere to describe explicitly the geodesic scattering on hyperboloids. It will be shown also that Knoerrer's reparametrisation is closely related to the projectively equivalent metric on a quadric discovered in 1998 by Tabachnikov and, independently, by Matveev and Topalov, giving a new proof of their result. The projectively equivalent metric (in contrast to the usual one) turns out to be regular on the projective closure of hyperboloid, which allows usto extend Knoerrer's map to this closure.
The talk is based on a recent joint work with Lihua Wu.[-]

The degenerate special Lagrangian equation governs geodesics in the space of positive Lagrangians. Existence of such geodesics has implications for uniqueness and existence of special Lagrangians. It also yields lower bounds on the cardinality of Lagrangian intersec- tions related to the strong Arnold conjecture. An overview of what is known about the existence problem will be given. The talk is based on joint work with A. Yuval and with Y. Rubinstein.[-]

To any algebraic differential equation, one can associate a first-order structure which encodes some of the properties of algebraic integrability and of algebraic independence of its solutions.To describe the structure associated to a given algebraic (nonlinear) differential equation (E), typical questions are:- Is it possible to express the general solutions of (E) from successive resolutions of linear differential equations?- Is it possible to express the general solutions of (E) from successive resolutions of algebraic differential equations of lower order than (E)?- Given distinct initial conditions for (E), under which conditions are the solutions associated to these initial conditions algebraically independent?In my talk, I will discuss in this setting one of the first examples of non-completely integrable Hamiltonian systems: the geodesic motion on an algebraically presented compact Riemannian surface with negative curvature. I will explain a qualitative model-theoretic description of the associated structure based on the global hyperbolic dynamical properties identified by Anosov in the 70's for the geodesic motion in negative curvature.[-]