Mathematical Physics Seminar Notes Lecture 1 Global Analysis and Lie Theory Wayne M. Lawton Department of Mathematics National University of Singapore 2 Science Drive 2 Singapore Tel (65)

Venue: S (Mathematics Conference Room B) Time: 16:00-17:15 Thursday 16 September Speaker: Wayne Lawton Title: Global Analysis and Lie Theory, talk 1 of Mathematical Physics Seminar Abstract: This talk will discuss material from and supplemental to that in Chapter 2 of Loop Groups by Pressley and Segal. We start by with the following observations: sections of the tangent bundle of a smooth manifold (vector fields) induce phase flows on the manifold, the set of sections forms an infinite dimensional Lie algebra,suitable sections of the Grassmann bundle (involutive distributions) induce foliations, and use these to develop the basic relationship between Lie groups and Lie algebras using the exponential mapping and the adjoint representation. We then review the linear algebra of unitary vector spaces and develop basic Lie theory: Schur's lemma, Killing form, roots, weights, Weyl group, induced representations, complex homogeneous spaces, and the Borel-Weil theorem. 2

Geometrization of Analysis based on Topology/Lie Theory – invented by Henri Poincare’/Sophus Lie for Differential Equations smooth manifold, navigate with coordinate charts 3 tangent space at a point is an equivalence class of ‘based’ smooth trajectories through the point

Tangent Bundle hence gives an isomorphism 4 defined by where is the equivalence class of Tangent Bundle of is topologized to give homeomorphisms together with the projection

Local Coordinates 5 is smooth hence where smooth functions onadmit local representation is smooth and whereis open

Vector Fields 6 is a smooth function that is a section, this means hence if on then

Fundamental Theorem of ODE’s 7 with induces a unique local flow and for furthermore, where applicable

Global Flows 8 and under suitable conditions, for example if is bounded then we obtain a smooth homomorphism then we obtain a smooth homomorphism of the group of real numbers into the group of diffeomorphisms of the manifold

Integral Trajectories 9 isan integral trajectory for Proof From the uniqueness part of the ODE theorem such that Theorem If c is an integral trajectory then Remark Ordinary Differential Equations by E. L. Ince references the work of Liouville, Cauchy, Lipschitz and others towards the modern ODE theorem

Grassmann Bundles over a Manifold and let 10 denote theDefinition Let d+1>k > 0, let Grassmann manifold of k-dimensional subspaces of be topologized in the local product manner. We will call this the Grassmann bundle over - it should not be confused with the Grassmann vector bundle over a Grassmann manifold whose fibers are subspaces – each fibers of this bundle is a Grassmann manifold !

Distributions 11 Definition A k-dimensional distribution on is a section of the Grassmann bundle over Definition A vector field is compatible with a distributionif

Fundamental Theorem of PDE’s 12 Lemmais closed under commutation Theorem (Frobenius) A distribution is integrable (admits a foliation into integral surfaces) iff it contains the commutator of every pair of vector fields that it contains. under which it is an infinite dimensional Lie algebra