The principle of simultaneous saturation: applications to multilinear models for the restriction and Bochner-Riesz problem

Abstract: We introduce a new technique for the fields of harmonic analysis and PDE, simultaneous saturation. Simultaneous saturation is a framework for controlling the size of a set where each element of the set is large. In this paper we apply this framework to multilinear restriction type estimates. Here the elements of the set are $Tf(p)$ where $T$ is an multilinear oscillatory integral operator. Controlling the size of the set where $Tf(p)$ is large allows us to obtain efficient $L^{p}$ estimates for the operator $T$. From this perspective we produce a new and independent of Bennett-Carbery-Tao \cite{BCT} proof of the multilinear restriction theorem. Further we then establish new results on multilinear models for the Bochner-Riesz problem that allow parameter dependent degeneration of the transversality condition.