Interacting Free Boundaries in the Calculus of Variations

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The goal of the project is to develop further the mathematical tools needed in the study of fundamental questions in nonlinear partial differential equations, calculus of variations, and free boundary problems. These questions have their origins in the applied sciences like elasticity, fluid mechanics, or cost optimization, and are relevant in areas of pure mathematics like geometry. The theoretical aspects of these models are important towards a better understanding of basic physical phenomena and could be useful for the larger scientific community. The project provides research training opportunities for students and its outcomes will be broadly disseminated to diverse audiences. The principal investigator (PI) will study several questions related to the classical obstacle problem. One of them concerns the multiple membrane problem, which describes the interaction of N elastic membranes in contact with each other. Mathematically, it can be viewed as a coupled system of obstacle problems with N-1 interacting free boundaries. Another question to be addressed deals with the uniqueness of certain blow-up cones for the thin obstacle problem, also known as the Signorini problem. An important part of the project considers the optimal transportation problem for quadratic costs with densities that vanish on the boundary of their support. This problem is equivalent to the second boundary value problem for a highly degenerate Monge-Ampère equation. The PI also aims to understand the interior regularity of minimizing maps in the calculus of variations for one of the simplest polyconvex energies in two dimensions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.