Comparison methods for semilinear elliptic problems on Riemannian manifolds with a Ricci lower bound

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Main Authors: Espinar, José M., González-Ibáñez, Fernán, Marín, Diego A.
Format: Preprint
Published: 2026
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author Espinar, José M.
González-Ibáñez, Fernán
Marín, Diego A.
author_facet Espinar, José M.
González-Ibáñez, Fernán
Marín, Diego A.
contents In the first part of the article we develop a comparison method for positive solutions of the semilinear Dirichlet problem $Δu+f(u)=0$ on domains $Ω\subset \mathcal M^n$ of a Riemannian manifold $(\mathcal{M}^n,g)$ with a Ricci lower bound $\operatorname{Ric}_g\ge (n-1)k\,g$. Assuming admissibility and structural conditions on $f$, we prove a sharp pointwise gradient comparison, with a rigid characterization of the equality case. As applications, we derive an explicit isoperimetric-type inequality and a quantitative hot-spot localization estimate under natural convexity assumptions. In the second part, on $\mathbb S^n$ we show that isoparametric foliations produce non-rotational $f$-extremal domains, and that these examples descend to smooth quotients under free isometric actions preserving the foliation.
format Preprint
id arxiv_https___arxiv_org_abs_2603_28479
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Comparison methods for semilinear elliptic problems on Riemannian manifolds with a Ricci lower bound
Espinar, José M.
González-Ibáñez, Fernán
Marín, Diego A.
Differential Geometry
Analysis of PDEs
35N25, 35J61, 53C21, 58J05
In the first part of the article we develop a comparison method for positive solutions of the semilinear Dirichlet problem $Δu+f(u)=0$ on domains $Ω\subset \mathcal M^n$ of a Riemannian manifold $(\mathcal{M}^n,g)$ with a Ricci lower bound $\operatorname{Ric}_g\ge (n-1)k\,g$. Assuming admissibility and structural conditions on $f$, we prove a sharp pointwise gradient comparison, with a rigid characterization of the equality case. As applications, we derive an explicit isoperimetric-type inequality and a quantitative hot-spot localization estimate under natural convexity assumptions. In the second part, on $\mathbb S^n$ we show that isoparametric foliations produce non-rotational $f$-extremal domains, and that these examples descend to smooth quotients under free isometric actions preserving the foliation.
title Comparison methods for semilinear elliptic problems on Riemannian manifolds with a Ricci lower bound
topic Differential Geometry
Analysis of PDEs
35N25, 35J61, 53C21, 58J05
url https://arxiv.org/abs/2603.28479