{"title":"Four Dimensional Hypersurfaces with Proper Mean Curvature Vector Field in Pseudo-Riemannian Space Forms","authors":"Chao Yang, Jiancheng Liu, Li Du","doi":"10.1007/s10114-026-4492-3","DOIUrl":"10.1007/s10114-026-4492-3","url":null,"abstract":"<div><p>In this paper, we prove that four-dimensional hypersurface <i>M</i><span>\u0000 <sup>4</sup><sub><i>r</i></sub>\u0000 \u0000 </span> with proper mean curvature vector field (i.e., <span>(Delta{vec H})</span> is proportional to <span>({vec H})</span>) in pseudo-Riemannian space form <i>N</i><span>\u0000 <sup>5</sup><sub><i>s</i></sub>\u0000 \u0000 </span>(<i>c</i>) has constant mean curvature, and give the value or range of this constant. As an application, we obtain that biharmonic hypersurfaces in <i>N</i><span>\u0000 <sup>5</sup><sub><i>s</i></sub>\u0000 \u0000 </span>(<i>c</i>) are minimal in some specific case.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"201 - 223"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339365","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":"Full Conformal Oscillator Representations of (mathfrak{o}(2n+2)) and Combinatorial Identities","authors":"Zhenyu Zhou","doi":"10.1007/s10114-026-4286-7","DOIUrl":"10.1007/s10114-026-4286-7","url":null,"abstract":"<div><p>Zhao and Xu (2013) constructed a functor from <span>(mathfrak{o}(n))</span>-<b>Mod</b> to <span>(mathfrak{o}(n+2))</span>-<b>Mod</b>. In this paper, we use the functor successively to obtain full conformal oscillator representation of <span>(mathfrak{o}(2n+2))</span> in <i>n</i>(<i>n</i> + 1) variables and determine the corresponding finite-dimensional irreducible module explicitly when the highest weight is dominant integral. We also find an equation of counting the dimension of an irreducible <span>(mathfrak{o}(2n+2))</span>-module in terms of certain alternating sum of the dimensions of irreducible <span>(mathfrak{o}(2n))</span>-modules, which leads to new combinatorial identities of classical type in the case of the Steinberg modules. One can use the results to study tensor decomposition of finite-dimensional irreducible modules by solving certain first-order linear partial differential equations, and thereby obtain the corresponding physically interested Clebsch–Gordan coefficients and exact solutions of Knizhnik–Zamolodchikov equation in WZW model of conformal field theory.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"1 - 49"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339363","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":"Study on Chaotic Behavior of the (N + 1)-Body Ring Problem","authors":"Xuhua Cheng, Mengqian Li","doi":"10.1007/s10114-026-4245-3","DOIUrl":"10.1007/s10114-026-4245-3","url":null,"abstract":"<div><p>In this paper, we study chaotic behavior of the (<i>N</i> + 1)-body planar ring problem. Firstly, based on the perturbation theory of integrable Hamiltonian systems, we utilize mass ratio as a disturbance parameter so that this ring problem is regarded as a perturbation of the two-body problem. Then, by applying the extended Melnikov method, we address that there are transversal homoclinic orbits in the ring problem. Afterwards, since the standard Smale–Birkhoff homoclinic theorem cannot be directly applied to the case of a degenerate saddle, we construct an invertible map <i>f</i> satisfying Conley–Moser condition and finally conclude that the ring problem possesses chaotic behavior of the Smale horseshoe type.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"189 - 200"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339459","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":"Bounded Directional Complexity and Rigidity for ℤq-actions","authors":"Runju Wei, Leiye Xu, Liqi Zheng, Xiaomin Zhou","doi":"10.1007/s10114-026-4222-x","DOIUrl":"10.1007/s10114-026-4222-x","url":null,"abstract":"<div><p>We introduce directional complexities for ℤ<sup><i>q</i></sup>-measure preserving dynamical systems via a collection of new metrics along non-zero directions in ℝ<sup><i>q</i></sup>. It turns out that a ℤ<sup><i>q</i></sup>-measure preserving dynamical system is rigid if and only if the invariant measure has bounded directional complexity. We also obtain ergodic decomposition formula for the measure-theoretic directional entropy of a ℤ<sup><i>q</i></sup>-measure preserving dynamical system.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"173 - 188"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10114-026-4222-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339460","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":"Quasi-stationary Distribution for the Explosive Single-birth Process","authors":"Zhekang Fang, Yonghua Mao, Yuhui Zhang","doi":"10.1007/s10114-026-4225-7","DOIUrl":"10.1007/s10114-026-4225-7","url":null,"abstract":"<div><p>For the minimal process corresponding to an explosive single-birth (or upwardly skip-free) <i>Q</i>-matrix on the non-negative integers, we prove the existence and uniqueness of quasi-stationary distribution, provide an explicit representation to it and show that it is the limit of quasi-stationary distributions of its truncated processes.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"151 - 172"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339463","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":"Derivatives of Local Times and Hausdorff Dimension of Inverse Images of Space-time Anisotropic Gaussian Random Fields","authors":"Peng Xu, Zhenlong Chen","doi":"10.1007/s10114-026-4355-y","DOIUrl":"10.1007/s10114-026-4355-y","url":null,"abstract":"<div><p>Let <i>X</i> = {<i>X</i>(<i>t</i>), <i>t</i> ∈ ∝<sup><i>N</i></sup>} be a centered space-time anisotropic Gaussian random field with values in ℝ<sup><i>d</i></sup>. Under some general conditions, the existence, joint continuity and Hölder conditions of higher-order derivative of local times of <i>X</i> are studied. Moreover, we obtain the uniform Hausdorff dimension of the inverse images of <i>X</i>. The existing results of Gaussian random fields are extended to space-time anisotropic Gaussian random fields with approximate independent components.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"224 - 238"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10114-026-4355-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339364","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":"Hardy Space Estimate of the Maximal Wave Operator","authors":"Jiecheng Chen, Dashan Fan, Junyan Zhao","doi":"10.1007/s10114-026-4215-9","DOIUrl":"10.1007/s10114-026-4215-9","url":null,"abstract":"<div><p>In this paper, we obtain the sharp Hardy space estimate of the maximal wave operator. Some applications on spherical averages and their combinations are also given.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"127 - 150"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339519","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":"Left-invariant Metrics on a Class of Solvable Lie Groups","authors":"Zhiqi Chen, Ke Yan, Hui Zhang","doi":"10.1007/s10114-026-4284-9","DOIUrl":"10.1007/s10114-026-4284-9","url":null,"abstract":"<div><p>Left-invariant Riemannian metrics on Lie groups <span>(G_{{{mathbb R}{rm H}}^{n-1}} times {mathbb R})</span> and <span>(G_{{{mathbb R}{rm H}}^{2}} times {{mathbb R}^{n-2}})</span> (<i>n</i> ≥ 3) have been classified by Hiroshi, Takahara and Tamaru. It is easily seen that <span>(G_{{{mathbb R}{rm H}}^{n-1}} times {mathbb R})</span> and <span>(G_{{{mathbb R}{rm H}}^{2}} times {{mathbb R}^{n-2}})</span> (<i>n</i> ≥ 3) have the same automorphism group, which is denoted by <i>L</i><sub><i>n</i></sub>. In this paper, we first classify <i>n</i>-dimensional simply connected Lie groups with automorphism group <i>L</i><sub><i>n</i></sub>, then we classify the left-invariant Riemannian metrics on such Lie groups. As an application, we get the <i>m</i>-quasi Einstein metrics.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"250 - 268"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339461","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":"Limit Theorems for Supercritical Remaining-lifetime Age-structured Branching Processes","authors":"Ziling Cheng","doi":"10.1007/s10114-026-4134-9","DOIUrl":"10.1007/s10114-026-4134-9","url":null,"abstract":"<div><p>We study supercritical age-structured branching models starting from a single particle with a random lifetime, where the reproduction law depends on the remaining lifetime of the parent. The lifespan of an individual is decided at its birth and its remaining lifetime decreases at the unit speed. A necessary and sufficient condition is provided for the convergence of the Malthusian normalized random measures. The Malthusian type limit theory in a functional form can be strengthened to hold with probability one under some “<i>L</i> log <i>L</i>” conditions. We further prove a central limit theory with a random normalization factor.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"50 - 84"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339462","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":"Generalized Turán Number for Edge Blow-up of Paths and Cycles","authors":"Yuanpei Wang, Liying Kang","doi":"10.1007/s10114-026-4223-9","DOIUrl":"10.1007/s10114-026-4223-9","url":null,"abstract":"<div><p>Given a graph <i>H</i> and an integer <i>p</i> ≥ 2, the edge blow-up graph <i>H</i><sup><i>p</i>+1</sup> of <i>H</i> is the graph obtained by replacing each edge in <i>H</i> with a clique of order <i>p</i> + 1, where the new vertices of the cliques are all distinct. The generalized Turán number ex(<i>n, K</i><sub><i>m</i></sub>, <i>F</i>) denote the maximum number of copies of <i>K</i><sub><i>m</i></sub> in an <i>n</i>-vertex <i>F</i>-free graph. Let <i>C</i><sub><i>t</i></sub> and <i>P</i><sub><i>t</i></sub> denote the cycle and path with <i>t</i> vertices, respectively. In this paper, we obtain the generalized Turán numbers ex(<i>n, K</i><sub><i>m</i></sub>, <i>P</i><span>\u0000 <sup><i>p</i>+1</sup><sub><i>t</i></sub>\u0000 \u0000 </span>), ex(<i>n, K</i><sub><i>m</i></sub>, <i>C</i><span>\u0000 <sup><i>p</i>+1</sup><sub><i>t</i></sub>\u0000 \u0000 </span>) and characterize the unique graph for <i>P</i><span>\u0000 <sup><i>p</i>+1</sup><sub><i>t</i></sub>\u0000 \u0000 </span> and <i>C</i><span>\u0000 <sup><i>p</i>+1</sup><sub><i>t</i></sub>\u0000 \u0000 </span> respectively, when <i>t</i> ≥ 3, <i>p</i> ≥ <i>m</i> ≥ 3 and <i>n</i> is sufficiently large.</p></div>","PeriodicalId":50893,"journal":{"name":"Acta Mathematica Sinica-English Series","volume":"42 1","pages":"239 - 249"},"PeriodicalIF":0.9,"publicationDate":"2026-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147339366","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}