A geometrical approach to the study of unbounded solutions of quasilinear parabolic equations

In this article, we are interested in the existence and uniqueness of solutions for quasilinear parabolic equations set in the whole space R-N. We consider, in particular, cases when there is no restriction on the growth or the behavior of these solutions at infinity. Our model equation is the mean-curvature equation for graphs for which Ecker and Huisken have shown the existence of smooth solutions for any locally Lipschitz continuous initial data. We use a geometrical approach which consists in seeing the evolution of the graph of a solution as a geometric motion which is then studied by the so-called "level-set approach". After determining the right class of quasilinear parabolic PDEs which can be taken into account by this approach, we show how the uniqueness for the original PDE is related to "fattening phenomena" in the level-set approach. Existence of solutions is proved using a local L-infinity bound obtained by using in an essential way the level-set approach. Finally we apply these results to convex initial data and prove existence and comparison results in full generality, i.e., without restriction on their growth at infinity.