{"title":"Conformal actions on the sphere with an open orbit","authors":"P. Ahmadi, M. Ahmadifard","doi":"10.1007/s10455-026-10030-x","DOIUrl":"10.1007/s10455-026-10030-x","url":null,"abstract":"<div><p>In this paper, we study conformal actions on the Euclidean sphere <span>(mathbb {S}^{n})</span>, focusing on the case where the action induces an open orbit. Under this condition, we determine the Lie algebras of the acting Lie groups up to conjugacy within the orthogonal group <i>O</i>(<i>n</i>, 1). Furthermore, we classify these actions up to orbit equivalence and specify the resulting orbits up to conformal equivalence.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147559311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Dynamics of Fuchsian meromorphic connections with real periods","authors":"Marco Abate, Karim Rakhimov","doi":"10.1007/s10455-026-10033-8","DOIUrl":"10.1007/s10455-026-10033-8","url":null,"abstract":"<div><p>In this paper, we study the dynamics of geodesics of Fuchsian meromorphic connections with real periods, giving a precise characterization of the possible <span>(omega )</span>-limit sets of simple geodesics in this case. The main tools are the study of the singular flat metric associated to the meromorphic connection, an explicit description of the geodesics nearby a Fuchsian pole with real residue larger than <span>(-1)</span> and a generalization to our case of the classical Teichmüller lemma for quadratic differentials.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441927","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the variety of Lie algebras endowed with complex structures: degenerations and deformations.","authors":"Edison Alberto Fernández-Culma, Nadina Rojas","doi":"10.1007/s10455-026-10034-7","DOIUrl":"10.1007/s10455-026-10034-7","url":null,"abstract":"<div><p>We study the space of Lie algebras equipped with left-invariant complex structures, <span>( mathcal {L}_{ J_{tiny {text{ cn }}} }(mathbb {R}^{2n}) )</span>, with particular attention to their degenerations and deformations. To this end, we identify certain invariants that remain well-behaved under degenerations while preserving the complex structure. These concepts are then applied to the four-dimensional case. Additionally, we explore applications to the study of left-invariant Hermitian structures on Lie groups, and we discuss some aspects of the deformation theory within <span>( mathcal {L}_{ J_{tiny {text{ cn }}} }(mathbb {R}^{2n}) )</span>.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Weak limits of the J-flow and the deformed Hermitian-Yang-Mills flow on Kähler surfaces: boundary cases","authors":"Rei Murakami","doi":"10.1007/s10455-026-10032-9","DOIUrl":"10.1007/s10455-026-10032-9","url":null,"abstract":"<div><p>We prove that if a pair of Kähler classes is <i>J</i>-nef, the <i>J</i>-flow on a compact Kähler surface converges to a weak solution of the Monge-Ampère equation in the sense of currents. We also establish the same convergence behavior for the deformed Hermitian-Yang-Mills flow. The method is based on a property of a limit of viscosity subsolutions.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10455-026-10032-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147441125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Positive Hermitian curvature flow on 2-step nilpotent Lie groups","authors":"Ettore Lo Giudice","doi":"10.1007/s10455-026-10031-w","DOIUrl":"10.1007/s10455-026-10031-w","url":null,"abstract":"<div><p>We study the positive Hermitian curvature flow for left-invariant metrics on 2-step nilpotent Lie groups <i>G</i> with a left-invariant complex structure <i>J</i>. We describe the long-time behavior of the flow under the assumption that <span>(J[mathfrak {g}, mathfrak {g}])</span> is contained in the center of <span>(mathfrak {g})</span>. We show that under our assumption the flow <span>(g_{t})</span> exists for all positive <i>t</i> and <span>((G,(1+t)^{-1}g_{t}))</span> converges, in the Cheeger-Gromov topology, to a 2-step nilpotent Lie group with a non flat semi-algebraic soliton. Moreover, we prove that, in our class of Lie groups, there exists at most one semi-algebraic soliton solution, up to homothety. Similar results were proved by M. Pujia and J. Stanfield for nilpotent complex Lie groups [21, 24]. In the last part of the paper we study the Hermitian curvature flow for the same class of Lie groups.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10455-026-10031-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147440982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hyperkähler ambient metrics associated with twistor CR manifolds","authors":"TAIJI MARUGAME","doi":"10.1007/s10455-026-10027-6","DOIUrl":"10.1007/s10455-026-10027-6","url":null,"abstract":"<div><p>Twistor CR manifolds, introduced by LeBrun, are Lorentzian (neutral) CR 5-manifolds defined as <span>(mathbb {P}^1)</span>-bundles over 3-dimensional conformal manifolds. In this paper, we embed a real analytic twistor CR manifold into the twistor space of the anti self-dual Poincaré-Einstein metric whose conformal infinity is the base conformal 3-manifold, and construct the associated Fefferman ambient metric as a neutral hyperkähler metric on the spinor bundle with the zero section removed. We also describe the structure of the Cheng–Yau type Kähler-Einstein metric which has the twistor CR manifold as the boundary at infinity.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The submanifold compatibility equations in magnetic geometry","authors":"Ivo Terek","doi":"10.1007/s10455-026-10026-7","DOIUrl":"10.1007/s10455-026-10026-7","url":null,"abstract":"<div><p>With the notions of magnetic curvature and magnetic second fundamental form recently introduced by Assenza and Albers–Benedetti–Maier, respectively, we establish analogues of the Gauss, Ricci, and Codazzi–Mainardi compatibility equations from submanifold theory in the magnetic setting.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 2","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10455-026-10026-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147336889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"(F_4) and desmic quartic surfaces","authors":"Laurent Manivel","doi":"10.1007/s10455-026-10028-5","DOIUrl":"10.1007/s10455-026-10028-5","url":null,"abstract":"<div><p>The desmic pencil of quartic surfaces is part of a beautiful, but mostly forgotten chapter of the classical theory of algebraic surfaces: it is the only non-degenerate pencil of quartic surfaces in <span>({mathbb {P}}^3)</span> containing at least three completely reducible members. We observe in this note that it is closely related to the Weyl group of the root system <span>(F_4)</span>, and can be recovered from a series of symmetric spaces deduced from the exceptional Lie algebras. We discuss the main properties of the pencil from this Lie theoretic point of view.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147335696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Heat coefficients of surfaces with curved conical singularities","authors":"Dorothee Schueth","doi":"10.1007/s10455-025-10024-1","DOIUrl":"10.1007/s10455-025-10024-1","url":null,"abstract":"<div><p>Let (<i>M</i>, <i>g</i>) be a two-dimensional Riemannian manifold of finite diameter with a conical singularity. Under the assumption that the metric near the cone point <i>C</i> is rotationally invariant, but not necessarily flat, we give an explicit formula for the coefficient <span>(b_{1/2}(C))</span> in the heat trace expansion <span>(operatorname {tr}(operatorname {exp}(-tDelta _g))sim _{tsearrow 0} (4pi t)^{-1}sum _{j=0}^infty a_j(M) t^j+sum _{j=0}^infty b_{j/2}(C)t^{j/2}+sum _{j=0}^infty c_{j/2}(C) t^{j/2} log t)</span>. In the case that the Gaussian curvature <i>K</i> of (<i>M</i>, <i>g</i>) satisfies <span>(|K(p)|rightarrow infty )</span> as <span>(prightarrow C)</span>, we show that <span>(b_{1/2}(C))</span> varies irrationally under constant rescalings of the distance circles near the cone point. This is a sharp contrast to the behavior of <span>(b_0(C))</span> and of those coefficients <span>(b_j(C))</span> which appear in certain known formulas in the case of orbifold cone points or corners of geodesic polygons.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145729883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Tetraplectic structures compatible with local quaternionic toric actions","authors":"Panagiotis Batakidis, Ioannis Gkeneralis","doi":"10.1007/s10455-025-10023-2","DOIUrl":"10.1007/s10455-025-10023-2","url":null,"abstract":"<div><p>This paper introduces a quaternionic analogue of toric geometry by developing the theory of local <span>( Q^n := textrm{Sp}(1)^n )</span>-actions on <span>( 4n )</span>-dimensional manifolds, modeled on the regular representation. We identify obstructions that measure the failure of local properties to globalize and define two invariants: a combinatorial invariant called the characteristic pair and a cohomological invariant called the Euler class, which together classify local quaternionic torus actions up to homeomorphism. We also study tetraplectic structures in quaternionic toric geometry by introducing locally generalized Lagrangian-type toric fibrations and show that such fibrations are locally modeled on <span>( mathbb {R}^n times Q^n )</span> using a quaternionic version of the Arnold–Liouville theorem. In the last part, we show that orbit spaces of these actions acquire the structure of quaternionic integral affine manifolds with corners and Lagrangian overlaps, and we classify such spaces by establishing a quaternionic Delzant-type theorem.</p></div>","PeriodicalId":8268,"journal":{"name":"Annals of Global Analysis and Geometry","volume":"69 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145449513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}