{"title":"On the Gradient of the Torsion Function for Elongated Cylinders.","authors":"M van den Berg","doi":"10.1007/s12220-026-02554-2","DOIUrl":"https://doi.org/10.1007/s12220-026-02554-2","url":null,"abstract":"<p><p>Let <math> <mrow><mrow><mo>(</mo> <mn>0</mn> <mo>,</mo> <mi>L</mi> <mo>)</mo></mrow> <mo>×</mo> <msub><mi>E</mi> <mi>a</mi></msub> <mo>⊂</mo> <msup><mrow><mi>R</mi></mrow> <mrow><mi>d</mi> <mo>+</mo> <mn>1</mn></mrow> </msup> </mrow> </math> denote the cylinder of length <i>L</i>, and base <math> <mrow><msub><mi>E</mi> <mi>a</mi></msub> <mo>⊂</mo> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> <mo>,</mo></mrow> </math> where <math><msub><mi>E</mi> <mi>a</mi></msub> </math> is an open ellipsoid with semi-axes <math><mrow><mi>a</mi> <mo>=</mo> <mo>(</mo> <msub><mi>a</mi> <mn>1</mn></msub> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>,</mo> <msub><mi>a</mi> <mi>d</mi></msub> <mo>)</mo></mrow> </math> . Let <math><msub><mi>w</mi> <mrow><mrow><mo>(</mo> <mn>0</mn> <mo>,</mo> <mi>L</mi> <mo>)</mo></mrow> <mo>×</mo> <msub><mi>E</mi> <mi>a</mi></msub> </mrow> </msub> </math> denote its torsion function. Heat equation tools are used to show that (i) if <math><msub><mi>E</mi> <mi>a</mi></msub> </math> has small eccentricity and <i>L</i> is sufficiently large, then the maxima of <math> <mrow><mrow><mo>|</mo> <mi>∇</mi></mrow> <msub><mi>w</mi> <mrow><mrow><mo>(</mo> <mn>0</mn> <mo>,</mo> <mi>L</mi> <mo>)</mo></mrow> <mo>×</mo> <msub><mi>E</mi> <mi>a</mi></msub> </mrow> </msub> <mrow><mo>|</mo></mrow> </mrow> </math> are located at the centres (0, 0) and (<i>L</i>, 0) respectively, (ii) if <math><msub><mi>E</mi> <mi>a</mi></msub> </math> has large eccentricity and <i>L</i> is sufficiently large, then the maxima are located on the lateral side of the cylinder.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"36 9","pages":"298"},"PeriodicalIF":1.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13401543/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148594766","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
João H Andrade, Jeffrey S Case, Paolo Piccione, Juncheng Wei
{"title":"A General Nonuniqueness Result for Yamabe-Type Problems for Conformally Variational Riemannian Invariants.","authors":"João H Andrade, Jeffrey S Case, Paolo Piccione, Juncheng Wei","doi":"10.1007/s12220-026-02598-4","DOIUrl":"https://doi.org/10.1007/s12220-026-02598-4","url":null,"abstract":"<p><p>Given a conformally variational scalar Riemannian invariant <i>I</i>, we identify a sufficient condition for a compact Riemannian manifold to admit finite regular coverings with many nonhomothetic conformal rescalings with <i>I</i> constant. We also identify a sufficient condition for the universal cover to admit infinitely many nonhomothetic periodic conformal rescalings with <i>I</i> constant. Using these conditions, we improve known nonuniqueness results for the <i>Q</i>-curvatures of orders two, four, and six. We also prove nonuniqueness results for higher-order <i>Q</i>-curvatures and renormalized volume coefficients.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"36 11","pages":"352"},"PeriodicalIF":1.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13562308/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148957368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carlo Alberto Antonini, Filomena De Filippis, Cintia Pacchiano Camacho
{"title":"On the Lavrentiev Gap for Manifold-Valued Maps.","authors":"Carlo Alberto Antonini, Filomena De Filippis, Cintia Pacchiano Camacho","doi":"10.1007/s12220-026-02628-1","DOIUrl":"https://doi.org/10.1007/s12220-026-02628-1","url":null,"abstract":"<p><p>We characterize necessary and sufficient conditions ensuring approximation by smooth maps in the Sobolev space <math><msup><mi>W</mi> <mrow><mn>1</mn> <mo>,</mo> <mi>φ</mi></mrow> </msup> </math> between suitable compact manifolds, where the prototypical example of Young function <math><mi>φ</mi></math> is the double-phase integrand.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"36 11","pages":"380"},"PeriodicalIF":1.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13645994/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149139419","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"<ArticleTitle xmlns:ns0=\"http://www.w3.org/1998/Math/MathML\">Free Boundary Hamiltonian Stationary Lagrangian Discs in <ns0:math> <ns0:msup><ns0:mrow><ns0:mi>C</ns0:mi></ns0:mrow> <ns0:mn>2</ns0:mn></ns0:msup></ns0:math>.","authors":"Filippo Gaia","doi":"10.1007/s12220-025-01962-0","DOIUrl":"https://doi.org/10.1007/s12220-025-01962-0","url":null,"abstract":"<p><p>Let <math><mrow><mi>Ω</mi> <mo>⊂</mo> <msup><mrow><mi>C</mi></mrow> <mn>2</mn></msup> </mrow> </math> be a smooth domain. We establish conditions under which a weakly conformal, branched <math><mi>Ω</mi></math> -free boundary Hamiltonian stationary Lagrangian immersion <i>u</i> of a disc in <math> <msup><mrow><mi>C</mi></mrow> <mn>2</mn></msup> </math> is a <math><mi>Ω</mi></math> -free boundary minimal immersion. We deduce that if <math><mi>u</mi></math> is a weakly conformal, branched <math> <mrow><msub><mi>B</mi> <mn>1</mn></msub> <mrow><mo>(</mo> <mn>0</mn> <mo>)</mo></mrow> </mrow> </math> -free boundary Hamiltonian stationary Lagrangian immersion of a disc with Legendrian boundary, then <math><mrow><mi>u</mi> <mo>(</mo> <msup><mi>D</mi> <mn>2</mn></msup> <mo>)</mo></mrow> </math> is a Lagrangian equatorial plane disc. Furthermore, we present examples of <math><mi>Ω</mi></math> -free boundary Hamiltonian stationary discs, demonstrating the optimality of our assumptions.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 5","pages":"160"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11971164/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143797164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Geometric Bounds for Low Steklov Eigenvalues of Finite Volume Hyperbolic Surfaces.","authors":"Asma Hassannezhad, Antoine Métras, Hélène Perrin","doi":"10.1007/s12220-025-01990-w","DOIUrl":"https://doi.org/10.1007/s12220-025-01990-w","url":null,"abstract":"<p><p>We obtain geometric lower bounds for the low Steklov eigenvalues of finite-volume hyperbolic surfaces with geodesic boundary. The bounds we obtain depend on the length of a shortest multi-geodesic disconnecting the surfaces into connected components each containing a boundary component and the rate of dependency on it is sharp. Our result also identifies situations when the bound is independent of the length of this multi-geodesic. The bounds also hold when the Gaussian curvature is bounded between two negative constants and can be viewed as a counterpart of the well-known Schoen-Wolpert-Yau inequality for Laplace eigenvalues. The proof is based on analysing the behaviour of the corresponding Steklov eigenfunction on an adapted version of thick-thin decomposition for hyperbolic surfaces with geodesic boundary. Our results extend and improve the previously known result in the compact case obtained by a different method.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 5","pages":"158"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11971064/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143797170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the Cheeger Inequality in Carnot-Carathéodory Spaces.","authors":"Martijn Kluitenberg","doi":"10.1007/s12220-025-01912-w","DOIUrl":"https://doi.org/10.1007/s12220-025-01912-w","url":null,"abstract":"<p><p>We generalize the Cheeger inequality, a lower bound on the first nontrivial eigenvalue of a Laplacian, to the case of geometric sub-Laplacians on rank-varying Carnot-Carathéodory spaces and we describe a concrete method to lower bound the Cheeger constant. The proof is geometric, and works for Dirichlet, Neumann and mixed boundary conditions. One of the main technical tools in the proof is a generalization of Courant's nodal domain theorem, which is proven from scratch for Neumann and mixed boundary conditions. Carnot groups and the Baouendi-Grushin cylinder are treated as examples.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 3","pages":"82"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11880090/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143574622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Joonas Ilmavirta, Antti Kykkänen, Matti Lassas, Teemu Saksala, Andrew Shedlock
{"title":"Lipschitz Stability of Travel Time Data.","authors":"Joonas Ilmavirta, Antti Kykkänen, Matti Lassas, Teemu Saksala, Andrew Shedlock","doi":"10.1007/s12220-025-02084-3","DOIUrl":"10.1007/s12220-025-02084-3","url":null,"abstract":"<p><p>We prove that the reconstruction of a certain type of length spaces from their travel time data on a closed subset is Lipschitz stable. The travel time data is the set of distance functions from the entire space, measured on the chosen closed subset. The case of a Riemannian manifold with boundary with the boundary as the measurement set appears is a classical geometric inverse problem arising from Gel'fand's inverse boundary spectral problem. Examples of spaces satisfying our assumptions include some non-simple Riemannian manifolds, Euclidean domains with non-trivial topology, and metric trees.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 8","pages":"244"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12206210/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144531301","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the Isoperimetric and Isodiametric Inequalities and the Minimisation of Eigenvalues of the Laplacian.","authors":"Sam Farrington","doi":"10.1007/s12220-024-01887-0","DOIUrl":"https://doi.org/10.1007/s12220-024-01887-0","url":null,"abstract":"<p><p>We consider the problem of minimising the <i>k</i>-th eigenvalue of the Laplacian with some prescribed boundary condition over collections of convex domains of prescribed perimeter or diameter. It is known that these minimisation problems are well-posed for Dirichlet eigenvalues in any dimension <math><mrow><mi>d</mi> <mo>≥</mo> <mn>2</mn></mrow> </math> and any sequence of minimisers converges to the ball of unit perimeter or diameter respectively as <math><mrow><mi>k</mi> <mo>→</mo> <mo>+</mo> <mi>∞</mi></mrow> </math> . In this paper, we show that the same is true in the case of Neumann eigenvalues under diameter constraint in any dimension and under perimeter constraint in dimension <math><mrow><mi>d</mi> <mo>=</mo> <mn>2</mn></mrow> </math> . We also consider these problems for Robin eigenvalues and mixed Dirichlet-Neumann eigenvalues, under an additional geometric constraint.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 2","pages":"62"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11811466/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143410705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Symbolic Calculus for a Class of Pseudodifferential Operators with Applications to Compactness.","authors":"Árpád Bényi, Tadahiro Oh, Rodolfo H Torres","doi":"10.1007/s12220-025-02128-8","DOIUrl":"https://doi.org/10.1007/s12220-025-02128-8","url":null,"abstract":"<p><p>We prove a symbolic calculus for a class of pseudodifferential operators, and discuss its applications to <math><msup><mi>L</mi> <mn>2</mn></msup> </math> -compactness via a compact version of the <i>T</i>(1) theorem.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 10","pages":"301"},"PeriodicalIF":1.5,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12325449/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144801046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Interpolating with generalized Assouad dimensions.","authors":"Amlan Banaji, Alex Rutar, Sascha Troscheit","doi":"10.1007/s12220-025-02099-w","DOIUrl":"10.1007/s12220-025-02099-w","url":null,"abstract":"<p><p>The <math><mi>ϕ</mi></math> -Assouad dimensions are a family of dimensions which interpolate between the upper box and Assouad dimensions. They are a generalization of the well-studied Assouad spectrum with a more general form of scale sensitivity that is often closely related to \"phase-transition\" phenomena in sets. In this article we establish a number of key properties of the <math><mi>ϕ</mi></math> -Assouad dimensions which help to clarify their behaviour. We prove for any bounded doubling metric space <i>F</i> and <math><mrow><mi>α</mi> <mo>∈</mo> <mi>R</mi></mrow> </math> satisfying <math> <mrow> <msub><mover><mtext>dim</mtext> <mo>¯</mo></mover> <mtext>B</mtext></msub> <mi>F</mi> <mo><</mo> <mi>α</mi> <mo>≤</mo> <msub><mtext>dim</mtext> <mtext>A</mtext></msub> <mi>F</mi></mrow> </math> that there is a function <math><mi>ϕ</mi></math> so that the <math><mi>ϕ</mi></math> -Assouad dimension of <i>F</i> is equal to <math><mi>α</mi></math> . We further show that the \"upper\" variant of the dimension is fully determined by the <math><mi>ϕ</mi></math> -Assouad dimension, and that homogeneous Moran sets are in a certain sense generic for these dimensions. Further, we study explicit examples of sets where the Assouad spectrum does not reach the Assouad dimension. We prove a precise formula for the <math><mi>ϕ</mi></math> -Assouad dimensions for the boundary of Galton-Watson trees that correspond to a general class of stochastically self-similar sets, including Mandelbrot percolation. The proof of this result combines a sharp large deviations theorem for Galton-Watson processes with bounded offspring distribution and a general Borel-Cantelli-type lemma for infinite structures in random trees. Finally, we obtain results on the <math><mi>ϕ</mi></math> -Assouad dimensions of overlapping self-similar sets and decreasing sequences with decreasing gaps.</p>","PeriodicalId":56121,"journal":{"name":"Journal of Geometric Analysis","volume":"35 9","pages":"270"},"PeriodicalIF":1.2,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12255623/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144638777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}