Wed, August 14, 2019
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4:00pm [4:00pm] Saikat Mazumdar:Mathematics Colloquium.
Mathematics Colloquium. Speaker: Saikat Mazumdar. Affiliation: IIT Bombay. Date and Time: Wednesday 14 August, 4:00 pm - 5:00 pm. Venue: Ramanujan Hall, Department of Mathematics. Title: Yamabe problem and beyond: an interplay of geometry and PDE. Abstract: Motivated by the theory of compact surfaces, Yamabe wanted to show that on a given compact Riemannian manifold of any dimension there always exists a (conformal) metric with constant scalar curvature. It turns out that solving the Yamabe problem amounts to solving a nonlinear elliptic partial differential equation (PDE). The solution of the Yamabe problem by Trudinger, Aubin and Schoen highlighted the local and global nature of the problem and the unexpected role of the positive mass theorem of general relativity. In the first part of my talk, I will survey the Yamabe problem and the related issues of the compactness of solutions. In the second part of the talk, I will discuss the higher-order or polyharmonic version of the Yamabe problem: "Given a compact Riemannian manifold (M, g), does there exists a metric conformal to g with constant Q-curvature?" The behaviour of Q-curvature under conformal changes of the metric is governed by certain conformally covariant powers of the Laplacian. The problem of prescribing the Q-curvature in a conformal class then amounts to solving a nonlinear elliptic PDE involving the powers of Laplacian called the GJMS operator. In general the explicit form of this GJMS operator is unknown. This together with a lack of maximum principle makes the problem difficult to tackle. I will present some of my results in this direction and mention some recent progress.