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Ellipsoidal Positivity Sets for Fractional Obstacle Problems with Quadratic Forcing
Abstract
Let n≥1, 0<s<1, c>0, and let A be a positive definite symmetric matrix. We prove that the unique decaying viscosity solution of min{u, (−Δ)s u−(c−⟨ Ax,x⟩)}=0 in ℝn has the form u(x)=Kmax{1−⟨ Bx,x⟩,0}1+s for some K>0 and some positive definite symmetric matrix B. In particular, its positivity set is an ellipsoid. For s=1/2 and n≥2, this result, combined with the classification of Fernández-Real and Yu, implies that cubic global thin obstacle solutions with nonempty bounded positivity set have ellipsoidal positivity sets. This proves the conjecture of Fernández-Real and Yu in the nonempty bounded-positivity case.
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BibTeX
@misc{kitano2026ellipsoidal,
title = {{Ellipsoidal Positivity Sets for Fractional Obstacle Problems with Quadratic Forcing}},
author = {Shuhei Kitano},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.00703},
eprint = {2609.00703},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.00703},
}
RIS
TY - UNPB
TI - Ellipsoidal Positivity Sets for Fractional Obstacle Problems with Quadratic Forcing
AU - Shuhei Kitano
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.00703
UR - https://arxiv.org/abs/2609.00703
AB - Let n≥1, 0<s<1, c>0, and let A be a positive definite symmetric matrix. We prove that the unique decaying viscosity solution of min{u, (−Δ)^s u−(c−⟨ Ax,x⟩)}=0 in ℝ^n has the form u(x)=Kmax{1−⟨ Bx,x⟩,0}^1+s for some K>0 and some positive definite symmetric matrix B. In particular, its positivity set is an ellipsoid. For s=1/2 and n≥2, this result, combined with the classification of Fernández-Real and Yu, implies that cubic global thin obstacle solutions with nonempty bounded positivity set have ellipsoidal positivity sets. This proves the conjecture of Fernández-Real and Yu in the nonempty bounded-positivity case.
ER -