arXiv subjects

Damião Araújo

Publications and source records attributed to Damião Araújo.

4 recordsLinked to original sources

arXiv2025

On free boundary problems shaped by varying singularities

We start the investigation of free boundary variational models featuring varying singularities. The theory depends strongly on the nature of the singular power $γ(x)$ and how it changes. Under a mild continuity assumption on $γ(x)$, we prove the optimal regularity of minimizers. Such estimates vary point-by-point, leading to a continuum of free boundary geometries. We also conduct an extensive analysis of the free boundary shaped by the singularities. Utilizing a new monotonicity formula, we show that if the singular power $γ(x)$ varies in a $W^{1,n^{+}}$ fashion, then the free boundary is locally a $C^{1,δ}$ surface, up to a negligible singular set of Hausdorff co-dimension at least $2$.

math.AP↗

arXiv2024

Regularity in diffusion models with gradient activation

We prove sharp regularity estimates for solutions of highly degenerate fully nonlinear elliptic equations. These are free boundary models in which a nonlinear diffusion process drives the system only in the region where the gradient surpasses a given threshold. Our main result concerns the existence of a universal modulus of continuity for $Du$, up to the free boundary. Gradient bounds for the $L^\infty$ norm are proven to be uniform with respect to the degree of degeneracy. Several new ingredients are needed and among the tools introduced in this paper is an improvement of regularity lemma designed to measure the oscillation decay concerning the gradient level-set distance. Applications of the methods are discussed at the end of the paper.

math.AP↗

arXiv2021

Sharp boundary and global regularity for degenerate fully nonlinear elliptic equations

We obtain optimal boundary and global regularity estimates for viscosity solutions of fully nonlinear elliptic equations whose ellipticity degenerates at the critical points of a given solution. We show that any solution is $C^{1,α}$ on the boundary of the domain, for an optimal and explicit $α$ given only in terms of the regularity of the boundary datum and the elliptic degeneracy degree, no matter how possibly low is the interior regularity for that class of equations. We also obtain sharp global estimates. Our findings are new even for model equations, involving only a degenerate Laplacian; all previous results of global nature give $C^{1,α}$ regularity only for some small $α>0$.

math.AP↗

arXiv2015

Geometric approach to nonvariational singular elliptic equations

In this work we develop a systematic geometric approach to study fully nonlinear elliptic equations with singular absorption terms as well as their related free boundary problems. The magnitude of the singularity is measured by a negative parameter $(γ-1)$, for $0 < γ< 1$, which reflects on lack of smoothness for an existing solution along the singular interface between its positive and zero phases. We establish existence as well sharp regularity properties of solutions. We further prove that minimal solutions are non-degenerate and obtain fine geometric-measure properties of the free boundary $\mathfrak{F} = \partial \{u > 0 \}$. In particular we show sharp Hausdorff estimates which imply local finiteness of the perimeter of the region $\{u > 0 \}$ and $\mathcal{H}^{n-1}$ a.e. weak differentiability property of $\mathfrak{F}$.

math.AP↗