That award praised his lucid, insightful, and influential reviews on partially conserved currents, gauge theories, instantons, and magnetic monopoles--subjects fundamental to theoretical physics.
en.wikipedia.org There he was involved in theoretical, experimental, and numerical work in theoretical physics, high-energy physics, nonlinear dynamics, fluid dynamics, nanotechnology, and robotics.
en.wikipedia.org Later in his career, he worked on solid-state physics, molecular physics, statistical physics, and other areas of theoretical physics.
en.wikipedia.org Although related to theoretical physics, mathematical physics in this sense emphasizes the mathematical rigour of the same type as found in mathematics.
en.wikipedia.org