## Lecture Course: Riemannian Geometry

Lecturer: Mehran Seyedhosseini

A Riemannian manifold is a manifold with a smooth choice of a scalar product on its tangent spaces (called a Riemannian metric). In this course, we will study some of the numerous concepts arising from this innocent looking extra piece of structure on a manifold. Here is an incomplete list of topics which will appear in the course (not necessarily in this order):

• We will define a distance function on the manifold using the Riemannian metric which makes the manifold into a metric space. We will discuss geodesics, which are the suitable generalisations of straight lines in the euclidean space, and geodesic completeness. The Hopf-Rinow theorem relating geodesic completeness and metric completeness will be proved.
• After a brief introduction to connections on the tangent and tensor bundles, we will prove the fundamental Theorem of Riemannian geometry, which states the existence of a connection, the so called Levi-Civita connection, with special properties. The Levi-Civita connection allows us to somewhat canonically identify tangent spaces at different points isometrically (parallel transport) and, as a result, to differentiate tensor fields on the manifold along vector fields (covariant differentiation).
• We will use the Levi-Civita connection to define one of the most important invariants of the Riemannian structure: the Riemannian curvature tensor. We will talk about its fundamental properties and the notions of Ricci and scalar curvature which can be extracted from it. We will talk about the relationship between curvature and geodesics.
• We will discuss some of the ways in which the curvature tensor of a Riemannian manifold can be used to obtain information about its topology (e.g. Synge and Myers' Theorem)
• Classification results for spaces with constant (sectional) curvature
• ...

The participants are expected to know the basics of multilinear algebra and analysis on manifolds.

The lectures will take place on Tuesdays and Fridays from 12:15 to 13:45.

For more information register here (Moodle page of the course). If you do not have a Moodle account, you can apply for one here.