Regularity and Stability for Solutions of Quasilinear Wave Equations with Singularities

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The formation of cusp and shock waves in optical systems, liquid crystals, and water waves are examples of nonlinear phenomena arising in nature and engineering that can be described by nonlinear partial differential equations. This project considers nonlinear partial differential equations for wave models whose solutions might form different types of singularities in finite time, such as cusp singularities in the shallow water wave equation or shock waves in models of nonlinear optics, with the overall aim of understanding under which condition the solutions are valid for all times. The research will give guidance in engineering, for example for designing and controlling devices in optical systems. The project will also provide opportunities for research training of graduate students. A main goal of the project is to describe how the power of nonlinear wave speed impacts the regularity of solutions. The investigator will study a class of equations, which include the short pulse equation from nonlinear optics and Camassa-Holm type equations from water waves, whose solutions might form finite-time singularities. They will also establish an optimal transport metric when studying the stability of a system of wave equations modelling nematic liquid crystals. Finally, they will explore a higher dimensional quasilinear model with radial symmetry, the so-called O(3) sigma-model, with background in general relativity, Yang-Mills field and nematic liquid crystals.This project is jointly funded by the DMS Applied Mathematics Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.