Special Session 70: Progress and Challenges in Nonlocal and Nonhomogeneous PDEs

Fractional Orlicz-Sobolev Spaces: Embeddings \& Continuity properties

Angela Alberico
Italian National Research Council - Institute for Applied Calculus (Napoli)
Italy
Co-Author(s):    Lubos Pick and Lenka Slavikova
Abstract:
The optimal target space is exhibited for embeddings of fractional-order Orlicz-Sobolev spaces. Both the subcritical and the supercritical regimes are considered. In the former case, the smallest possible Orlicz target space is detected. In the latter, the relevant Orlicz-Sobolev spaces are shown to be embedded into the space of bounded continuous functions in $\mathbb R^n$. Moreover, their optimal modulus of continuity is exhibited. These results are the subject of a series of joint papers with Andrea Cianchi, Lubo\v s Pick and Lenka Slav\'ikov\'a.

Regularity results and maximum principles for quasilinear operators of mixed local-nonlocal type

Carlo Alberto Antonini
INdAM (National Institute of High Mathematics)
Italy
Co-Author(s):    
Abstract:
In this talk, we will deal with mixed local-nonlocal quasilinear operators, modeled upon the sum of a $p$-Laplacian and a fractional $(s,q)$-Laplace operator, i.e., $-\Delta_p u+(-\Delta_q)^s u$. We will review some recent results concerning local and global regularity of their solutions, and we will address the validity of maximum principles and Hopf Lemma for such operators. Based on a series of joint works with M. Cozzi and P. Baroni.

Irregular double-phase evolution problem: Existence and Global regularity

Rakesh Arora
Indian Institute of Technology, Varanasi
India
Co-Author(s):    Sergey Shmarev
Abstract:
This talk presents the existence and regularity results of the homogeneous Dirichlet problem involving the double-phase operator with variable exponents, non-differentiable modulating coefficients and the free term $f$. We establish the existence of a strong solution, which preserves initial temporal integrability, gains global higher integrability and improves second-order regularity.

DOUBLE PHASE PROBLEMS WITH EXPONENTS DEPENDING ON SOLUTIONS AND THEIR GRADIENTS

Anouar Bahrouni
University of Monastir
Tunisia
Co-Author(s):    Ala Eddine Bahrouni and Hlel Missaoui
Abstract:
In this talk,, we introduce two novel classes of quasilinear elliptic equations, each driven by the double phase operator with variable exponents. The first class features a new double phase equation where exponents depend on the gradient of the solution. In the second category, the treatment of exponents is dependent on the solution itself. This class differs from the first one due to the unavailability of suitable Musielak-Orlicz Sobolev spaces. For this reason, we employ a perturbation argument that leads to the classical double phase class.

ON UNBOUNDED SOLUTIONS OF ERGODIC PROBLEMS FOR NON-LOCAL HAMILTON-JACOBI EQUATIONS

Cristina Brandle
U. Carlos III de Madrid
Spain
Co-Author(s):    Emmanuel Chasseigne
Abstract:
We study an ergodic problem associated to a non-local Hamilton-Jacobi equation defined on the whole space $\lambda-\mathcal{L}[u](x)+|D u(x)|^m=f(x)$ and determine whether (unbounded) solutions exist or not. We prove that there is a threshold growth of the function $f$, that separates existence and non-existence of solutions, a phenomenon that does not appear in the local version of the problem. Moreover, we show that there exists a critical ergodic constant, $\lambda_*$, such that the ergodic problem has solutions for $\lambda \leqslant \lambda_*$ and such that the only solution bounded from below, which is unique up to an additive constant, is the one associated to $\lambda_*$.

On the weak Harnack inequality for a generalized Orlicz De Giorgi class

simone ciani
University of Bologna Alma Mater
Italy
Co-Author(s):    Eurica Henriques, Igor I. Skrypnik
Abstract:
We introduce a generalization of De Giorgi classes with Orlicz growth. The aim is twofold: on the one hand, to encompass a broader class of functionals and equations; on the other hand, to provide a definition based on a simple energy inequality that does not rely on an underlying functional, but rather on the intrinsic scaling between radii and levels. For these classes, we establish a Weak Harnack inequality, thereby unifying its validity across non-uniformly elliptic equations, double-phase and degenerate double-phase functionals, as well as functionals with variable exponents.

No pain, no gain on critical logarithmic double phase equations

Alessio Fiscella
Universidade Estadual de Campinas
Brazil
Co-Author(s):    
Abstract:
In this talk, we discuss about double phase equations set in $\mathbb R^N$ involving critical Sobolev terms and logarithmic perturbations. By variational methods, we provide different existence results for our equations. The main difficulties arise from the presence of the logarithmic perturbation, which is sign-changing, combined with a double lack of compactness, due to the free action of translation group in $\mathbb R^N$ and the critical Sobolev nonlinearity. Furthermore, we have to deal with the Luxemburg type norm of the solution space, which complicates even the study of geometry for the energy functional. Our results, contained in https://doi.org/10.1016/j.jmaa.2025.129311 and in https://doi.org/10.1007/s00030-025-01172-1, are new even in the classical $p$-Laplacian case.

Wiener criterion for nonlocal and nonhomogeneous equations

Minhyun Kim
Hanyang University
Korea
Co-Author(s):    Ki-Ahm Lee, Se-Chan Lee
Abstract:
In this talk, we present the Wiener criterion for nonlocal equations with Orlicz growth, which provides a necessary and sufficient condition for boundary points to be regular. Our approach relies on the fine analysis of superharmonic functions in view of nonlocal nonlinear potential theory. Especially, the Wolff potential estimates play a fundamental role.

On polyharmonic double phase problems

Tuhina Mukherjee
Indian Institute of Technology Jodhpur
India
Co-Author(s):    Ashutosh Dixit
Abstract:
This talk shall be on study of higher-order doubly critical elliptic problems with weights, driven by a polyharmonic double phase operator. Precisely, problems of the type \begin{equation*} \begin{cases} \mathcal{L}^m_{p,q}(u) = f(x,u) ~&\text{in } \Omega,\ u=\nabla u=\cdots\nabla^{m-1} u=0 &\text{on }{\partial\Omega}, \end{cases} \end{equation*} where $\Omega \subset \mathbb{R}^N$ with $N \geq 2$ is a smooth bounded domain with Lipschitz boundary $\partial\Omega$, $m \in \mathbb{N}$, $1 < p < q < \frac{N}{m}$ with $(N-1)q\leq Np$, the nonlinear term $f\colon\Omega\times\mathbb{R}\to \mathbb{R}$ is Caratheodary function, which has doubly critical growth, and $\mathcal{L}^m_{p,q}$ represents a polyharmonic double phase operator. I shall present suitable Musielak--Orlic--Sobolev framework to study such problems, through application of variational methods. The existence of weak solutions can be derived by establishing a compactness result within these spaces and in addition, the nonexistence results can also be derived under appropriate assumptions by establishing a Pohozaev-type identity for higher-order derivatives. The overall approach is an extension of classical techniques to capture the intricate features of the double phase operator for higher-order derivatives, and shall address the difficulties arising from critical nonlinearities, while also overcoming the non closed feature of truncations in higher order Sobolev spaces.

Periodically perforated energies in the nonlocal setting

Giampiero Palatucci
University of Parma
Italy
Co-Author(s):    Matteo Focardi; Caterina Ida Zeppieri
Abstract:
We study the asymptotic behavior of fractional Dirichlet energies in periodically perforated domains via De Giorgi's Gamma-convergence. In the critical regime, we identify the so-called strange term in the spirit of Cioranescu and Murat. The proof relies on a mesoscopic annular freezing procedure, localized fractional capacitary estimates, and a bulk decoupling argument controlling the nonlocal interactions. We also characterize the subcritical and supercritical regimes: in the former the perforations are asymptotically invisible, while in the latter bounded-energy sequences collapse to zero.

On a Sobolev critical problemfor the superposition of a local and nonlocal operator with the wrong sign

Eugenio Vecchi
ALMA MATER STUDIORUM - Universita' di Bologna
Italy
Co-Author(s):    
Abstract:
In this talk I will focus on a Sobolev critical problems in a bounded domain where the operator is given by th $-\Delta - (-\Delta)^s$ with $s\in (0,1)$, possibly losing the maximum principles. I will discuss the existence of at least one non trivial solution. The talk is based on a joint work with S. Biagi, S. Dipierro and E. Valdinoci.