### Wael Abdelhedi

Qassim University, Buraidah, Saudi Arabia### Hichem Hajaiej

California State University, Los Angeles, USA### Zeinab Mhamdi

Sfax University, Tunisia

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## Abstract

In this paper, we consider the nonlinear fractional critical equation with zero Dirichlet boundary condition $A_s u= K u^\frac{n+2s}{n-2s}$, $u>0$ in $\Omega$ and $u=0$ on $\partial\Omega$, where $K$ is a positive function, $\Omega$ is a regular bounded domain of $\mathbb{R}^n$, $n\geq 2$ and $A_s$, $s\in (0,1)$ represents the spectral fractional Laplacian operator $(-\Delta)^s$ in $\Omega$ with zero Dirichlet boundary condition. We prove a version of Morse lemmas at infinity for this problem. We also exhibit a relevant application of our novel result. More precisely, we characterize the critical points at infinity of the associated variational problem and we prove an existence result for $s=\frac{1}{2}$ and $n=3$.

## Cite this article

Wael Abdelhedi, Hichem Hajaiej, Zeinab Mhamdi, A Morse lemma at infinity for nonlinear elliptic fractional equations. Rend. Sem. Mat. Univ. Padova 146 (2021), pp. 1–42

DOI 10.4171/RSMUP/82