Searcharxiv⌕ Search

arXiv subjects

Cristiana De Filippis

Publications and source records attributed to Cristiana De Filippis.

At least 19 recordsLinked to original sources
arXiv2026

Light rays of Lorentzian graphs and the Born-Infeld model

Following a program outlined by Bartnik, and also employing nonlinear potential techniques we developed in the last years, we study lightlike singularities of variational solutions to the prescribed Lorentzian mean curvature equation with possibly unbounded (rough) curvature. This corresponds to allowing for unbounded charges in the Born-Infeld model.

math.AP↗
arXiv2026

Necessity of Ladyzhenskaya \& Ural'tseva's sufficient conditions in nonuniform ellipticity

The sufficient conditions of Ladyzhenskaya \& Ural'tseva \cite{lu70} for interior gradient estimates in nonuniformly elliptic problems are found to be also necessary. Specifically, nonparametric minimal surfaces exhibit the maximal nonuniformity rate compatible with the local Lipschitz regularity of solutions, and the classical theory of Finn \cite{fin54} and Bombieri \& De Giorgi \& Miranda \cite{bdm69} doesn't extend beyond Bernstein genre $2$.

math.AP↗
arXiv2026

Partial regularity in nonlocal systems I

Solutions to nonlinear integro-differential systems are regular outside a negligible closed subset whose Hausdorff dimension can be explicitly bounded from above. This subset can be characterized using quantitative, universal energy thresholds for nonlocal excess functionals. The analysis is carried out via the use of nonlinear potentials and allows to derive fine properties of solutions under sharp assumptions on data and kernel coefficients.

math.AP↗
arXiv2026

Intrinsic Schauder estimates at nearly linear growth

We develop a nonlinear potential theoretic framework for Schauder estimates for vector-valued solutions of a broad class of nonautonomous variational problems at nearly linear growth. Our approach naturally embraces the variable exponent as well as the Double and Multi phase setting, yielding new regularity results in basic models and recovering optimal regularity recently established in specific cases.

math.AP↗
arXiv2026

Partial regularity in nonlocal systems II

Solutions to nonlinear nonlocal systems of order $2s>1$ in $\mathbb{R}^n$ are $C^{1,α}$, for every $α<2s-1$, outside a closed singular set whose Hausdorff dimension is less than $n-2$, and which is empty when $n=2$.

math.AP↗
arXiv2026

Coarse-grained ellipticity and De Giorgi-Nash-Moser theory

We prove local boundedness and a Harnack inequality for nonnegative weak solutions of the equation $-\nabla\cdot(\mathbf{a}(x)\nabla u)=0$ under a coarse-grained ellipticity assumption on the symmetric coefficient field $\mathbf{a}$. Coarse-grained ellipticity is a scale-dependent condition, defined for fields with only $\mathbf{a},\mathbf{a}^{-1}\in L^1$, in terms of families of effective diffusion matrices on triadic cubes of all sizes, and our estimates depend quantitatively on a corresponding coarse-grained ellipticity ratio. We show that coarse-grained ellipticity can be enforced by purely negative Sobolev regularity hypotheses: if $\mathbf{a}\in L^1\cap W^{-s,p}(U)$ and $\mathbf{a}^{-1}\in L^1\cap W^{-t,q}(U)$ for exponents $p,q\in[1,\infty]$ and $s,t\in[0,1)$ satisfying $s<1-\frac{1}{p}$, $t<1-\frac{1}{q}$ and \[ \frac{s+t}{2} + \frac{d}{2}\Bigl(\frac{1}{p}+\frac{1}{q}\Bigr) < 1, \] then $\mathbf{a}$ is coarse-grained elliptic in $U$ and every nonnegative solution satisfies a quantitative unit-scale Harnack inequality. In particular, when $s=t=0$ we recover Trudinger's classical result under the integrability condition $\mathbf{a}\in L^p$, $\mathbf{a}^{-1}\in L^q$ with $\frac{1}{p}+\frac{1}{q}<\frac{2}{d}$, and we obtain the sharp scaling of the Harnack constant in terms of $\|\mathbf{a}\|_{L^p}$ and $\|\mathbf{a}^{-1}\|_{L^q}$. More importantly, our criteria apply to new classes of degenerate and singular coefficient fields for which $\mathbf{a},\mathbf{a}^{-1}\notin L^{1+δ}$ for all $δ>0$, including examples generated by singular fractal measures and Gaussian multiplicative chaos, beyond the reach of previous approaches based solely on integrability assumptions.

math.AP↗
arXiv2025

$μ$-ellipticity and nonautonomous integrals

$μ$-ellipticity is a form of nonuniform ellipticity arising in various contexts from the calculus of variations. Understanding regularity properties of minimizers in the nonautonomous setting is a challenging task fostering the development of delicate techniques and the discovery of new irregularity phenomena.

math.AP↗
arXiv2025

Sketches of Nonuniformly Elliptic Schauder Theory

Schauder theory is a basic tool in the study of elliptic and parabolic PDEs, asserting that solutions inherit the regularity of the coefficients. It plays a central role in establishing higher regularity for solutions to a broad class of elliptic problems exhibiting ellipticity, including those involving free boundaries. In the linear setting, Schauder theory dates back to the 1920-30s and is now considered classical. Nonlinear extensions were developed in the 1980s. All these classical results are restricted to uniformly elliptic operators and heavily rely on perturbative techniques - freezing the coefficients and comparing the solution to that of a constant-coefficient problem. However, such methods fail in the nonuniformly elliptic setting, where homogeneous a priori estimates break down and standard iteration arguments no longer apply. Here we give a brief survey on recent progresses including the solution to the longstanding problem of proving the validity of Schauder estimates in the nonlinear, nonuniformly elliptic setting.

math.AP↗
arXiv2024

Quantified Legendreness and the regularity of minima

We introduce a new quantification of nonuniform ellipticity in variational problems via convex duality, and prove higher differentiability and $2d$-smoothness results for vector valued minimizers of possibly degenerate functionals. Our framework covers convex, anisotropic polynomials as prototypical model examples - in particular, we improve in an essentially optimal fashion Marcellini's original results \cite{ma1}.

math.AP↗
arXiv2023

Regularity for double phase problems at nearly linear growth

Minima of functionals of the type $$ w\mapsto \int_Ω\left[\snr{Dw}\log(1+\snr{Dw})+a(x)\snr{Dw}^{q}\right] \dx\,, \quad 0\leq a(\cdot) \in C^{0, α}\,,$$ with $Ω\subset \er^n$, have locally Hölder continuous gradient provided $1 < q < 1+α/n$.

math.AP↗
arXiv2022

Borderline global regularity for nonuniformly elliptic systems

We establish sharp global regularity results for solutions to nonhomogeneous, nonunifomrly elliptic systems with zero boundary conditions. In particular, we obtain everywhere Lipschitz continuity under borderline Lorentz assumptions on the forcing term, thus positively settling the optimality issue raised in \cite{bdms}.

math.AP↗
arXiv2022

Quasiconvexity and partial regularity via nonlinear potentials

We show how to infer sharp partial regularity results for relaxed minimizers of degenerate, nonuniformly elliptic quasiconvex functionals, using tools from Nonlinear Potential Theory. In particular, in the setting of functionals with $(p,q)$-growth - according to the terminology of Marcellini [52] - we derive optimal local regularity criteria under minimal assumptions on the data.

math.AP↗
arXiv2022

Singular multiple integrals and nonlinear potentials

We prove sharp partial regularity criteria of nonlinear potential theoretic nature for the Lebesgue-Serrin-Marcellini extension of nonhomogeneous singular multiple integrals featuring $(p,q)$-growth conditions.

math.AP↗