2025/07/18 by Gatti, Michele, Scheuer, Julian, Weth, Tobias
#35B35 (Secondary) #35N25 #35R11 (Primary) 35B06 #Analysis of PDEs (math.AP) #FOS: Mathematics
paper · doi:10.48550/arxiv.2507.13715
We investigate symmetry and quantitative approximate symmetry for an overdetermined problem related to the fractional torsion equation in a regular open, bounded set Ω⊆ ℝn. Specifically, we show that if Ω has positive reach and the nonlocal normal derivative introduced in (Dipierro, Ros-Oton, Valdinoci, Rev. Mat. Iberoam. 33 (2017), no. 2, 377-416) is constant on an external surface parallel and sufficiently close to ∂ Ω, then Ω must be a ball. Remarkably, this conclusion remains valid under the sole assumption that Ω is convex. Moreover, we analyze the quantitative stability of this result under two distinct sets of assumptions on Ω. Finally, we extend our analysis to a broader class of overdetermined Dirichlet problems involving the fractional Laplacian.