Georg Frenck, Jan-Bernhard Kordaß
In this paper we study spaces of Riemannian metrics with lower bounds on intermediate curvatures. We show that the spaces of metrics of positive p-curvature and k-positive Ricci curvature on a given high-dimensional Spin-manifold have many non-trivial homotopy groups provided that the manifold admits such a metric.
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On the topology of manifolds with positive intermediate curvature
本文研究正$m$-中间曲率与流形万有覆盖拓扑的关系，证明了低维及六维多数情形的猜想，并推出闭非球面6维流形不存在正$4$-中间曲率度量。
In a recent work of Brendle-Hirsch-Johne, a notion of intermediate curvature was introduced to extend the classical non-existence theorem of positive scalar curvature on torus to product manifolds. In this work, we study the rigidity when the intermediate curvature is only non-negative when the ambient dimension is at most $5$.
Positive Intermediate Ricci Curvature on Fibre Bundles
本文证明了浸没度量的典型变分型结果，结合手术技术为高连通流形和 exotic 球面等例子建立了正中间里奇曲率度量的存在性，并将正里奇曲率模空间结果推广至正中间情形。
We prove the existence of elements of infinite order in the homotopy groups of the spaces $\mathcal{R}_{Ric>0}(M)$ and $\mathcal{R}_{sec>0}(M)$ of positive Ricci and positive sectional curvature, provided that $M$ is high-dimensional and Spin, admits such a metric and has a non-vanishing rational Pontryagin class.
For dimensions $n\geq 3$ and $k\in\{2, \cdots, n\}$, we show that the space of metrics of $k$-positive Ricci curvature on the sphere $S^{n}$ has the structure of an $H$-space with a homotopy commutative, homotopy associative product operation. We further show, using the theory of operads and results of Boardman, Vogt and May that the path component of this space containing the round metric is weakly homotopy equivalent to an $n$-fold loop space.
We use a local argument to prove if an $r$-dimensional torus acts isometrically and effectively on a connected $n$-dimensional manifold which has positive $k^\mathrm{th}$-intermediate Ricci curvature at some point, then $r \leq \lfloor \frac{n+k}{2} \rfloor$. This symmetry rank bound generalizes those established by Grove and Searle for positive sectional curvature and Wilking for quasipositive curvature. As a consequence, we show that the symmetry rank bound in the Maximal Symmetry Rank Conjecture for manifolds of non-negative sectional curvature holds for those which also have positive inter…
We use the cobordism category constructed in arXiv:1703.01047 to the study the homotopy type of the space of positive scalar curvature metrics on a spin manifold of dimension > 4. Our methods give an alternative proof and extension of a recent theorem of Botvinnik, Ebert, and Randal-Williams from arXiv:1411.7408.
Positive intermediate Ricci curvature with maximal symmetry rank
该研究推广了Grove和Searle的工作，证明了正中间里奇曲率流形等距群秩的上界，并在最大对称秩情形下获得更强的拓扑刚性结果，涵盖更高曲率及非平凡基本群。
A generalization of the Perelman gluing theorem and applications
本文将Perelman正Ricci曲率粘合定理推广到从正标量曲率到正截面曲率的正中间曲率条件，并应用于证明观察者模空间具有非平凡高阶同伦群及给出带全测地边界的正中间Ricci曲率度量存在性充分条件。
Nonexistence of the metric with positive intermediate curvatures on manifolds with boundary
本文证明维数不超过7的紧致带边流形在边界$m$-凸时不能有正$m$-中间曲率度量，并推广了相关结果到带边情形。
Comparison Theorems and the Intermediate Ricci Curvature Assumption
本文进一步研究了 m-中间 Ricci 曲率假设，证明了在非负 m-中间 Ricci 曲率及稳定加权切片条件下，最后一切片在谱意义下几乎非负，并给出了此类流形中切片直径与内径界的比较定理。
In arXiv:2207.08617 [math.DG] Brendle-Hirsch-Johne proved that $T^m\times S^{n-m}$ does not admit metrics with positive $m$-intermediate curvature when $n\leq 7$. Chu-Kwong-Lee showed in arXiv:2208.12240 [math.DG] a corresponding rigidity statement when $n\leq 5$. In this paper, we show the sharpness of the dimension constraints by giving concrete counterexamples in $n\geq 7$ and extending the rigidity result to $n=6$. Concerning uniformly positive intermediate curvature, we show that simply-connected manifolds with dimension $\leq 5$ and bi-Ricci curvature $\geq 1$ have finite Urysohn 1-width…
Positive intermediate Ricci curvature on cohomogeneity one manifolds in low dimensions
研究闭低维等余一流形上具有正中间 Ricci 曲率的不变度量的存在性，对特定作用构造了正第4中间 Ricci 曲率度量并证明不能有正第3中间 Ricci 曲率度量，同时建立了类似对称性障碍。
Local Topology of Riemannian Manifolds with Lower Intermediate Ricci Curvature Bounds
本文证明了在体积、直径和中间里奇曲率下界条件下，闭流形局部贝蒂数的消失定理，并推广至开流形的全局贝蒂数。
We prove that every quasitoric manifold admits an invariant metric of positive scalar curvature.
In this paper we consider a well-known construction due to Gromov and Lawson, Schoen and Yau, Gajer, and Walsh which allows for the extension of a metric of positive scalar curvature over the trace of a surgery in codimension at least $3$ to a metric of positive scalar curvature which is a product near the boundary. We generalize this construction to work for $(p,n)$-intermediate scalar curvature for $0\leq p\leq n-2$ for surgeries in codimension at least $p+3$. We then use it to generalize a well known theorem of Carr. Letting ${\cal R}^{s_{p,n}>0}(M)$ denote the space of positive $(p, n)$-in…
The Log-Sobolev inequality for a submanifold in manifolds with asymptotic non-negative intermediate Ricci curvature
本文在具有渐近非负中间里奇曲率和欧氏体积增长的完备非紧黎曼流形上，证明了子流形的尖锐对数-Sobolev不等式，推广了Dong-Lin-Lu等人的已有结果。
Fixed Point Homogeneous Orbifolds with Positive Sectional Curvature
本文对等变微分同胚下具有正截面曲率的不动点齐性黎曼轨形分类，进而得到具极大对称秩的正曲率轨形分类结果。
Optimal Transport Approach to Michael-Simon-Sobolev Inequalities in Manifolds with Intermediate Ricci Curvature Lower Bounds
该研究将最优输运的McCann定理推广至子流形场景，证明了满足中间Ricci曲率下界条件的流形内子流形的Michael-Simon-Sobolev不等式，涵盖了已有相关研究结论的变体情形。
Homological $k$-systole in $n$-manifolds with positive intermediate curvature
研究3到7维具有正中间曲率的闭n维黎曼流形，证明最优k-收缩不等式并刻画等式情形，统一并扩展前人工作，受中间曲率分裂定理工作启发得出结论。
Preserving positive intermediate curvature
本文证明在第二基本形式满足 $m$-正差条件时，两个正 $m$-中间曲率度量可由同类型度量光滑连接，并据此得到严格 $m$-凸部分环面带的不存在性结论。
Jacobian estimates and geometric inequalities under intermediate Ricci curvature
本文证明了一个适用于任意余维子流形的 Jacobian 估计，无需曲率符号假设，并由此在中间 Ricci 曲率条件下推导出定量 Fenchel--Willmore、Sobolev 和等周不等式，所需条件仅与子流形维数相关。
We show $ 10/8$-type inequalities for some end-periodic $4$-manifolds which have positive scalar curvature metrics on the ends. As an application, we construct a new family of closed $4$-manifolds which do not admit positive scalar curvature metrics.
Positive intermediate Ricci curvature on connected sums
研究正$k^{th}$中间Ricci曲率下连通和的构造问题，提出$k$-核度量概念并证明线性球丛连通和在特定$k$值范围内允许该曲率，同时给出$\mathbb{H} P^n$和$\mathbb{O}P^2$的最优核度量实例。
Odd-dimensional manifolds with infinitely many different geometries of positive Ricci curvature
针对n≥5的奇数维闭流形，证明其存在无限多个不同的正Ricci曲率几何，即正Ricci曲率度量模空间有无限多个连通分支，丰富了奇数维流形正Ricci曲率几何的研究。
On Hopf's conjecture and positive second intermediate Ricci curvature
针对正第二中间 Ricci 曲率下 Hopf 猜想结论可能失效的问题，本文证明维数被四整除且具有秩至少十的环面对称性时，Euler 示性数为正，并推广了 Four Periodicity Theorem。
In this short note we discuss some recent results about two-positive Ricci curvature and their applications to positive Einstein curvature.
Lower Bound for Weighted Intermediate Ricci Curvature and Tensorial Entropy Convexity
本研究引入加权中间里奇曲率，建立其下界的等价刻画，推广相关结果并对比不同学者的刻画，为几何分析领域提供了新的理论进展。
In this paper we show that for Riemannian manifolds with boundary the natural restriction map is a quasifibration between spaces of metrics of positive scalar curvature. We apply this result to study homotopy properties of spaces of such metrics on manifolds with boundary.
We classify, up to homeomorphisms, the closed simply-connected 4-manifolds that admit a Riemannian metric for which averages of pairs of sectional curvatures of orthogonal planes are positive.
We establish metrics of positive $2^\mathrm{nd}$-intermediate Ricci curvature, i.e. $\mathrm{Ric}_2>0$, on products of positively curved homogeneous spaces. Using these examples, we demonstrate that the Hopf conjectures, Petersen-Wilhelm conjecture, Berger fixed point theorem, and Hsiang-Kleiner theorem for positively curved manifolds do not hold in the $\mathrm{Ric}_2>0$ setting. These observations indicate that the class of manifolds with $\mathrm{Ric}_2>0$ is vastly different from the class of positively curved manifolds.
We show that the higher homotopy groups of the moduli space of torus-invariant positive scalar curvature metrics on certain quasitoric manifolds are non-trivial.
We study closed, simply connected manifolds with positive $2^\mathrm{nd}$-intermediate Ricci curvature and large symmetry rank. In odd dimensions, we show that they are spheres. In even dimensions other than $6$, we show that they must have positive Euler characteristic. Under stronger assumptions on the symmetry rank, we show that such even dimensional manifolds must have trivial odd degree integral cohomology, and if the second Betti number is no more than $1$, they are either spheres or complex projective spaces. In the process, we establish new tools for studying isometric actions on close…
Fenchel-Willmore-Chen inequality under lower bounds on weighted intermediate Ricci curvature
针对具1-Bakry-Émery k-里奇曲率下界的光滑度量测度空间，建立Fenchel-Willmore-Chen不等式并给出统一证明，同时证明非负1-加权里奇曲率的Sobolev与等周不等式。
Minimal Two-Spheres and Manifolds with Positive Isotropic Curvature
本文改进调和二维球面的指标估计至锐界$n-3$，结合近期工作完成五维和六维正迷向曲率闭流形的微分同胚分类。
We show that the homotopy type of the space of metrics of positive scalar curvature on a smooth manifold remains unchanged, after application of surgery in codimension at least three to the underlying manifold. This result is originally due to V. Chernysh, but remains unpublished.
Intermediate Ricci curvatures and Gromov's Betti number bound
本文研究闭黎曼流形上的中间 Ricci 曲率 $Ric_k$，通过建立 $Ric_k>0$ 度量的手术结果，证明在指定 $k$ 范围内 Gromov 的 Betti 数上界失效，并将此前正 Ricci 曲率的结论推广。
We show an equivariant bordism principle for constructing metrics of positive scalar curvature that are invariant under a given group action. Furthermore, we develop a new codimension-2 surgery technique which removes singular strata from fixed point free $S^1$-manifolds while preserving equivariant positive scalar curvature. These results are applied to derive the following generalization of a result of Gromov and Lawson: Each closed fixed point free $S^1$-manifold of dimension at least 6 whose isotropy groups have odd order and whose union of maximal orbits is simply connected and not spin c…
We introduce Riemannian metrics of positive scalar curvature on manifolds with Baas-Sullivan singularities, prove a corresponding homology invariance principle and discuss admissible products. Using this theory we construct positive scalar curvature metrics on closed smooth manifolds of dimension at least five which have odd order abelian fundamental groups, are nonspin and atoral. This solves the Gromov-Lawson-Rosenberg conjecture for a new class of manifolds with finite fundamental groups.
We prove the existence of Sasakian metrics with positive Ricci curvature on certain highly connected odd dimensional manifolds. In particular, we show that manifolds homeomorphic to the 2k-fold connected sum of S^{2n-1} x S^{2n} admit Sasakian metrics with positive Ricci curvature for all k. Furthermore, a formula for computing the diffeomorphism types is given and tables are presented for dimensions 7 and 11.
Sobolev inequalities in manifolds with nonnegative intermediate Ricci curvature
本文利用Alexandrov-Bakelman-Pucci方法，将Michael-Simon型Sobolev不等式推广到具有非负中间Ricci曲率的Riemannian流形中的子流形上，并由此导出极小子流形的等周不等式。
We give a complete classification of homogeneous $(α,β)$-metrics with positive flag curvature and vanishing S-curvature.
Constant Rank Theorems under Intermediate Ricci Curvature
针对具有调和曲率的流形和梯度里奇孤子，证明当1≤k≤n-2时k阶中间里奇曲率非负可推出里奇张量常秩，且该k范围最优，仅非负里奇曲率无法保证常秩。
If $π:M\rightarrow B$ is a Riemannian Submersion and $M$ has positive sectional curvature, O'Neill's Horizontal Curvature Equation shows that $B$ must also have positive curvature. We show there are Riemannian submersions from compact manifolds with positive Ricci curvature to manifolds that have small neighborhoods of (arbitrarily) negative Ricci curvature, but that there are no Riemannian submersions from manifolds with positive Ricci curvature to manifolds with nonpositive Ricci curvature.
We show that after forming a connected sum with a homotopy sphere, all (2j-1)-connected 2j-parallelisable manifolds in dimension 4j+1, j > 0, can be equipped with Riemannian metrics of 2-positive Ricci curvature. The condition of 2-positive Ricci curvature is defined to mean that the sum of the two smallest eigenvalues of the Ricci tensor is positive at every point. This result is a counterpart to a previous result of the authors concerning the existence of positive Ricci curvature on highly connected manifolds in dimensions 4j-1 for j > 1, and in dimensions 4j+1 for j > 0 with torsion-free co…
In this note, we prove that for a complete noncompact three dimensional Riemannian manifold with bounded sectional curvature, if it has uniformly positive scalar curvature, then there is a uniform lower bound on the injectivity radius.
Positive scalar curvature on manifolds with boundary and their doubles
本文研究了紧致带边界流形上正数量曲率度量的边界条件与其加倍流形正数量曲率问题之间的关系，在某些情形下给出了完整回答。
We begin a systematic study of a curvature condition (strongly positive curvature) which lies strictly between positive curvature operator and positive sectional curvature, and stems from the work of Thorpe in the 1970s. We prove that this condition is preserved under Riemannian submersions and Cheeger deformations, and that most compact homogeneous spaces with positive sectional curvature satisfy it.
In this paper, we mainly study the mean curvature flow in Kähler surfaces with positive holomorphic sectional curvatures. We prove that if the ratio of the maximum and the minimum of the holomorphic sectional curvatures is less than 2, then there exists a positive constant $δ$ depending on the ratio such that $\cosα\geqδ$ is preserved along the flow.
We classify homogeneous reversible Finsler metrics with positive Flag curvature. We show that if G/H admits a G invariant reversible Finsler metric with positive Flag curvature, then up to a few low dimensional spaces, it also admits a G invariant Riemannian metric with positive sectional curvature. For the exceptions, we do not know if they admit homogeneous Finsler metrics with positive Flag curvature.
In this paper, we study the topological rigidity and its relationship with the positivity of scalar curvature. Precisely, we show that any complete contractible $3$-manifold with non-negative scalar curvature is homeomorphic to $\mathbf{R}^3$.
Intermediate curvature and splitting theorem
本文证明了非紧致完备流形在非负中间曲率下的刚性结果，展示特定条件下流形可被标准积结构覆盖，并构造了具有均匀正中间曲率的光滑度量，证明了代数条件的精确性。
In this paper, we give a new generalization of positive sectional curvature called positive weighted sectional curvature. It depends on a choice of Riemannian metric and a smooth vector field. We give several simple examples of Riemannian metrics which do not have positive sectional curvature but support a vector field that gives them positive weighted curvature. On the other hand, we generalize a number of the foundational results for compact manifolds with positive sectional curvature to positive weighted curvature. In particular, we prove generalizations of Weinstein's theorem, O'Neill's fo…
We prove the weak stability of expanding gradient Ricci solitons with positive curvature operator and quadratic curvature decay at infinity.
In a previous paper, we constructed complete manifolds of positive Ricci curvature with quadratically asymptotically nonnegative curvature and infinite topological type but dimension $\ge 6$. The purpose of the present paper is to use a different way to exhibit a family of complete $I$-dimensinal ($I\ge5$) Riemannian manifolds of positive Ricci curvature, quadratically asymptotically nonnegative sectional curvature, and certain infinite Betti number $b_j$ ($2\le j\le I-2$).
Volume Growth under Positive Intermediate Curvature and a Ricci Lower Bound
该研究针对满足里奇下界与正中间曲率的完备黎曼流形，通过分析Fisher特征值，得到了不同尺度下球的体积增长估计，并证明了大尺度下指数因子的必要性。
In this paper we prove a compactness theorem for constant mean curvature surfaces with area and genus bound in three manifold with positive Ricci curvature. As an application, we give a lower bound of first eigenvalue of constant mean curvature surfaces in three manifold with positive Ricci curvature.
Riemannian metrics of positive Ricci curvature were constructed on certain moment-angle manifolds.
We construct metrics of positive Ricci curvature on some vector bundles over tori (or more generally, over nilmanifolds). This gives rise to the first examples of manifolds with positive Ricci curvature which are homotopy equivalent but not homeomorphic to manifolds of nonnegative sectional curvature.
The goal of the paper is to give an optimal transport characterization of sectional curvature lower (and upper) bounds for smooth $n$-dimensional Riemannian manifolds. More generally we characterize, via optimal transport, lower bounds on the so called $p$-Ricci curvature which corresponds to taking the trace of the Riemann curvature tensor on $p$-dimensional planes, $1\leq p\leq n$. Such characterization roughly consists on a convexity condition of the $p$-Renyi entropy along $L^{2}$-Wasserstein geodesics, where the role of reference measure is played by the $p$-dimensional Hausdorff measure.…
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