Boundary regularity of minima
Jan Kristensen, Giuseppe Mingione · Rendiconti Lincei Matematica e Applicazioni · 2008
Let u: Ω → ℝ^N be any given solution to the Dirichlet variational problem \min\limits{w} ∫_Ω F(x,w,Dw) dx,\quad w ≡ u_0 \quad\text{on } ∂Ω, where the integrand F(x,w,Dw) is strongly convex in the gradient variable Dw , and suitably Hölder continuous with respect to (x,w) . We prove that almost every boundary point, in the sense of the usual surface measure of ∂Ω , is a regular point for u . This means that Du is Hölder continuous in a relative neighborhood of the point. The existence of even one of such regular boundary points was an open problem for the general functionals considered here, and known only under certain very special structure assumptions.