Bernis estimates for higher-dimensional doubly-degenerate non-Newtonian thin-film equations

TL;DR

This paper derives Bernis estimates for higher-dimensional doubly-degenerate non-Newtonian thin-film equations, providing key inequalities that facilitate the analysis of solutions' existence, support propagation, and waiting-time phenomena.

Contribution

It extends Bernis estimates to a class of nonlinear, higher-order, doubly-degenerate non-Newtonian thin-film equations in multiple dimensions.

Findings

Established local Bernis estimates for the equations.

Derived a key gradient estimate for solutions.

Facilitated proofs of solution existence and support properties.

Abstract

For the doubly-degenerate parabolic non-Newtonian thin-film equation $$ u_t + \text{div}\bigl(u^n |\nabla \Delta u|^{p-2} \nabla \Delta u\bigr) = 0, $$ we derive (local versions) of Bernis estimates of the form $$ \int_{\Omega} u^{n-2p} |\nabla u|^{3p}\, dx + \int_{\Omega} u^{n-\frac{p}{2}} |\Delta u|^{\frac{3p}{2}}\, dx \leq c(n,p,d) \int_{\Omega} u^n|\nabla \Delta u|^p\, dx, $$ for functions $u \in W^2_p(\Omega)$ with Neumann boundary condition, where $2 \leq p < \frac{19}{3}$ and $n$ lies in a certain range. Here, $\Omega \subset \mathbb{R}^d$ is a smooth convex domain with $d < 3p$. A particularly important consequence is the estimate $$ \int_{\Omega} |\nabla \Delta (u^{\frac{n+p}{p}})|^p\, dx \leq c(n,p,d) \int_{\Omega} u^n|\nabla \Delta u|^p\, dx. $$ The methods used in this article follow the approach of [Gr\"u01] for the Newtonian case, while addressing the specific challenges posed by the nonlinear higher-order term $|\nabla \Delta u|^{p-2} \nabla \Delta u$ and the additional degeneracy. The derived estimates are key to establishing further qualitative results, such as the existence of weak solutions, finite propagation of support, and the appearance of a waiting-time phenomenon.