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Eduardo V. Teixeira

Publications and source records attributed to Eduardo V. Teixeira.

At least 37 records · Page 2Linked to original sources
arXiv2022

On the sharp Hessian integrability conjecture in the plane

We prove that if $u\in C^0(B_1)$ satisfies $F(x,D^2u) \le 0$ in $B_1\subset \mathbb{R}^2$, in the viscosity sense, for some fully nonlinear $(λ, Λ)$-elliptic operator, then $u \in W^{2,\varepsilon}(B_{1/2})$, with appropriate estimates, for a sharp exponent $ \varepsilon = \varepsilon(λ, Λ)$ verifying $$ \frac{1.629}{\fracΛλ + 1} < \varepsilon(λ, Λ) \le \frac{2}{\fracΛλ + 1}, $$ uniformly as $\fracλΛ \to 0$. This is closely related to the Armstrong-Silvestre-Smart conjecture, raised in [Comm. Pure Appl. Math. 65 (2012), no. 8, 1169--1184], where the upper bound is postulated to be the optimal one.

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arXiv2022

New regularity estimates for fully nonlinear elliptic equations

We establish new quantitative Hessian integrability estimates for viscosity supersolutions of fully nonlinear elliptic operators. As a corollary, we show that the optimal Hessian power integrability $\varepsilon = \varepsilon(λ, Λ, n)$ in the celebrated $W^{2, \varepsilon}$-regularity estimate satisfies $$\frac{ \left (1+ \frac{2}{3}\left(1- \fracλΛ \right )\right )^{n-1}}{\ln n^4} \cdot \left( \fracλΛ \right) ^{n-1} \le \varepsilon \le \frac{nλ}{(n-1)Λ+λ}, $$ where $n\ge 3$ is the dimension and $0< λ< Λ$ are the ellipticity constants. In particular, $\left( \fracΛλ \right) ^{n-1} \varepsilon(λ, Λ, n)$ blows-up, as $n\to\infty$; previous results yielded fast decay of such a quantity. The upper estimate improves the one obtained by Armstrong, Silvestre, and Smart in arXiv:1103.3677

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arXiv2022

On the Bernoulli problem with unbounded jumps

We investigate Bernoulli free boundary problems prescribing infinite jump conditions. The mathematical set-up leads to the analysis of non-differentiable minimization problems of the form $\int \left(\nabla u\cdot (A(x)\nabla u) + φ(x) 1_{\{u>0\}}\right) \,\mathrm{d}x \to \text{min}$, where $A(x)$ is an elliptic matrix with bounded, measurable coefficients and $φ$ is not necessarily locally bounded. We prove universal Hölder continuity of minimizers for the one- and two-phase problems. Sharp regularity estimates along the free boundary are also obtained. Furthermore, we perform a thorough analysis of the geometry of the free boundary around a point $ξ$ of infinite jump, $ξ\in φ^{-1}(\infty)$. We show that it is determined by the blow-up rate of $φ$ near $ξ$ and we obtain an analytical description of such cusp geometries.

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arXiv2022

$C^1$-regularity for degenerate diffusion equations

We prove that any solution of a degenerate elliptic PDE is of class $C^1$, provided the inverse of the equation's degeneracy law satisfies an integrability criterium, viz. $σ^{-1} \in L^1\left (\frac{1}λ {\bf d}λ\right )$. The proof is based upon the construction of a sequence of converging tangent hyperplanes that approximate $u(x)$, near $x_0$, by an error of order $\text{o}(|x-x_0|)$. Explicit control of such hyperplanes is carried over through the construction, yielding universal estimates upon the ${C}^1$--regularity of solutions. Among the main new ingredients required in the proof, we develop an alternative recursive algorithm for the renormalization of approximating solutions. This new method is based on a technique tailored to prevent the sequence of degeneracy laws constructed through the process from being, itself, degenerate.

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arXiv2022

Fractional Sobolev regularity for fully nonlinear elliptic equations

We prove higher-order fractional Sobolev regularity for fully nonlinear, uniformly elliptic equations in the presence of unbounded source terms. More precisely, we show the existence of a universal number $0< \varepsilon <1$, depending only on ellipticity constants and dimension, such that if $u$ is a viscosity solution of $F(D^2u) = f(x) \in L^p$, then $u\in W^{1+\varepsilon,p}$, with appropriate estimates. Our strategy suggests a sort of fractional feature of fully nonlinear diffusion processes, as what we actually show is that $F(D^2u) \in L^p \implies (-Δ)^θu \in L^p$, for a universal constant $\frac{1}{2} < θ<1$. We believe our techniques are flexible and can be adapted to various models and contexts.

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arXiv2020

On a continuous Gale--Berlekamp switching game

We propose a continuous version of the classical Gale--Berlekamp switching game. We also study a weighted version of this new continuous game. The main results of this paper concern growth estimates for the corresponding optimization problems. The methods developed in this article are deterministic in nature and in some special cases the estimates obtained are optimal.

math.CO↗
arXiv2020

Free boundary problems involving singular weights

In this paper we initiate the investigation of free boundary minimization problems ruled by general singular operators with $A_2$ weights. We show existence and boundedness of minimizers. The key novelty is a sharp $C^{1+γ}$ regularity result for solutions at their singular free boundary points. We also show a corresponding non-degeneracy estimate.

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arXiv2019

Reflexivity and non-weakly null maximizing sequences

We introduce and explore a new property related to reflexivity that plays an important role in the characterization of norm attaining operators. We also present an application to the theory of compact perturbations of linear operators and characterize norm attaining scalar-valued continuous $2$-homogeneous polynomials on $\ell_{2}$.

math.FA↗
arXiv2019

Geometric tangential analysis and sharp regularity for degenerate pdes

We provide a broad overview on qualitative versus quantitative regularity estimates in the theory of degenerate parabolic pdes. The former relates to DiBenedetto's revolutionary method of intrinsic scaling, while the latter is achieved by means of what has been termed geometric tangential analysis. We discuss, in particular, sharp estimates for the parabolic p-Poisson equation, for the porous medium equation and for the doubly nonlinear equation.

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arXiv2019

A proof of the $C^{p^\prime}$-regularity conjecture in the plane

We establish a new oscillation estimate for solutions of nonlinear partial differential equations of elliptic, degenerate type. This new tool yields a precise control on the growth rate of solutions near their set of critical points, where ellipticity degenerates. As a consequence, we are able to prove the planar counterpart of the longstanding conjecture that solutions of the degenerate $p$-Poisson equation with a bounded source are locally of class $C^{p^\prime}=C^{1,\frac{1}{p-1}}$; this regularity is optimal.

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arXiv2018

Regularity of solutions to a class of variable-exponent fully nonlinear elliptic equations

In the present paper, we propose the investigation of variable-exponent, degenerate/singular elliptic equations in non-divergence form. This current endeavor parallels the by now well established theory of functionals satisfying nonstandard growth condition, which in particular encompasses problems ruled by the $p(x)$-laplacian operator. Under rather general conditions, we prove viscosity solutions to variable exponent fully nonlinear elliptic equations are locally of class $C^{1,κ}$ for a universal constant $0< κ< 1$. A key feature of our estimates is that they do not depend on the modulus of continuity of exponent coefficients, and thus may be employed to investigate a variety of problems whose ellipticity degenerates and/or blows-up in a discontinuous fashion.

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arXiv2016

Regularity principle in sequence spaces and applications

We prove a nonlinear regularity principle in sequence spaces which produces universal estimates for special series defined therein. Some consequences are obtained and, in particular, we establish new inclusion theorems for multiple summing operators. Of independent interest, we settle all Grothendieck's type $(\ell_{1},\ell_{2})$ theorems for multilinear operators. We further employ the new regularity principle to solve the classification problem concerning all pairs of admissible exponents in the anisotropic Hardy--Littlewood inequality.

math.CA↗
arXiv2016

Nonlinear elliptic equations with high order singularities

We study non-variational degenerate elliptic equations with high order singular structures. No boundary data are imposed and singularities occur along an {\it a priori} unknown interior region. We prove that positive solutions have a universal modulus of continuity that does not depend on their infimum value. We further obtain sharp, quantitative regularity estimates for non-negative limiting solutions.

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arXiv2016

Sharp regularity estimates for second order fully nonlinear parabolic equations

We prove sharp regularity estimates for viscosity solutions of fully nonlinear parabolic equations of the form \begin{equation}\label{Meq}\tag{Eq} u_t- F(D^2u, Du, X, t) = f(X,t) \quad \mbox{in} \quad Q_1, \end{equation} where $F$ is elliptic with respect to the Hessian argument and $f \in L^{p,q}(Q_1)$. The quantity $κ(n, p, q):=\frac{n}{p}+\frac{2}{q}$ determines to which regularity regime a solution of \eqref{Meq} belongs. We prove that when $1< κ(n,p,q) < 2-ε_F$, solutions are parabolic-Hölder continuous for a sharp, quantitative exponent $0< α(n,p,q) < 1$. Precisely at the critical borderline case, $κ(n,p,q)= 1$, we obtain sharp Log-Lipschitz regularity estimates. When $0< κ(n,p,q) <1$, solutions are locally of class $C^{1+ σ, \frac{1+ σ}{2}}$ and in the limiting case $κ(n,p,q) = 0$, we show $C^{1, \text{Log-Lip}}$ regularity estimates provided $F$ has "better" \textit{a priori} estimates.

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arXiv2016

Infinity Laplacian equation with strong absorptions

We study regularity properties of solutions to reaction-diffusion equations ruled by the infinity laplacian operator. We focus our analysis in models presenting plateaus, i.e. regions where a non-negative solution vanishes identically. We obtain sharp geometric regularity estimates for solutions along the boundary of plateaus sets. In particular we show that the $(n-ε)$-Hausdorff measure of the plateaus boundary is finite, for a universal number $ε>0$.

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arXiv2015

Cavity problems in discontinuous media

We study cavitation type equations, $\text{div}(a_{ij}(X) \nabla u) \sim δ_0(u)$, for bounded, measurable elliptic media $a_{ij}(X)$. De Giorgi-Nash-Moser theory assures that solutions are $α$-Hölder continuous within its set of positivity, $\{u>0\}$, for some exponent $α$ strictly less than one. Notwithstanding, the key, main result proven in this paper provides a sharp Lipschitz regularity estimate for such solutions along their free boundaries, $\partial \{u>0 \}$. Such a sharp estimate implies geometric-measure constrains for the free boundary. In particular, we show that the non-coincidence $\{u>0\}$ set has uniform positive density and that the free boundary has finite $(n- ς)$-Hausdorff measure, for a universal number $0< ς\le 1$.

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arXiv2015

Optimal design problems with fractional diffusions

In this article we study optimization problems ruled by $α$-fractional diffusion operators with volume constraints. By means of penalization techniques we prove existence of solutions. We also show that every solution is locally of class $C^{0,α}$ (optimal regularity), and that the free boundary is a $C^{1,γ}$ surface, up to a $\mathcal{H}^{n-1}$-negligible set.

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