This paper proves properties of CAT(κ) surfaces with bounded curvature.
problem Properties of CAT(κ) surfaces with bounded curvature.
method Proof of bounded curvature, approximation by smooth surfaces.
result CAT(κ) surfaces have bounded curvature.
The study glues CAT(0) subsets of the plane under certain curvature conditions.
problem Understanding how to combine locally CAT(0) spaces. method Describes a gluing process for subsets of the Euclidean plane that maintain the CAT(0) property. result The gluing of two CAT(0) subsets, under specific curvature conditions, results in another CAT(0) space. In this paper, we show some splitting theorems for CAT(0) spaces on which a product group acts geometrically and we obtain a splitting theorem for compact geodesic spaces of non-positive curvature. A CAT(0) group Γ is said to be {\it rigid}, if Γ determines the boundary up to homeomorphisms of a CAT(0) space on whi…
Quantifies Schur's theorem for curves in CAT(k) spaces.
problem Quantifying Schur's comparison theorem for curves in CAT(k) spaces.
method Comparison formula for curves in model planes, curvature measures, moment arm, and Reshetnyak's theorem.
result Sharpens and extends classical arm and bow lemmas and Riemannian analogues.
4-manifolds with non-positive curvature are essentially Euclidean.
problem Understanding the structure of 4-manifolds with specific curvature properties.
method Proving homeomorphism to Euclidean space using globally non-positive curvature.
result CAT(0) 4-manifolds are homeomorphic to Euclidean space.
We study the curvature of metric spaces and branched covers of Riemannian manifolds, with applications in topology and algebraic geometry. Here curvature bounds are expressed in terms of the CAT(k) inequality. We prove a general CAT(k) extension theorem, giving sufficient conditions on and near the boundary of a locall…
We examine volume pinching problems of CAT(1) spaces. We characterize a class of compact geodesically complete CAT(1) spaces of small specific volume. We prove a sphere theorem for compact CAT(1) homology manifolds of small volume. We also formulate a criterion of manifold recognition for homology manifolds on volume g…
The study finds multiple solutions for constant Q-curvature metrics.
problem Finding multiple metrics with constant Q-curvature.
method Proving subcritical equations have at least Cat(M) positive solutions.
result Proves existence of at least Cat(M) metrics with constant Q-curvature.
In this article, I prove that full subcomplexes of CAT(0) simplicial 3-complexes inherit the non positive curvature condition, and describe a family of counterexamples that prove this result can not be extended to higher dimensions.
We construct examples of smooth 4-dimensional manifolds M supporting a locally CAT(0)-metric, whose universal cover X satisfy Hruska's isolated flats condition, and contain 2-dimensional flats F with the property that the boundary at infinity of F defines a nontrivial knot in the boundary at infinity of X. As a consequ…
Let (M,g) be any closed Riemannianan manifold and (N,h) be a Riemannian manifold of constant positive scalar curvature. We prove that the Yamabe equation on the Riemannian product (M×N,g+δh) has at least Cat(M)+1 solutions for δ small enough, where Cat(M) denotes the Lusternik-Schnirelmann-categ…
Let K be a 2-dimensional finite flag complex. We study the CAT(0) dimension of the `Bestvina-Brady group', or `Artin kernel', Gamma_K. We show that Gamma_K has CAT(0) dimension 3 unless K admits a piecewise Euclidean metric of non-positive curvature. We give an example to show that this implication cannot be reversed. …
We study analytic properties of harmonic maps from Riemannian polyhedra into CAT(κ) spaces for κ∈{0,1}. Locally, on each top-dimensional face of the domain, this amounts to studying harmonic maps from smooth domains into CAT(κ) spaces. We compute a target variation formula that captures the curvature bound in…
Paper shows equivalence of two curvature notions on singular surfaces.
problem Equivalence of two curvature notions on singular surfaces.
method Demonstrates equivalence between two curvature definitions.
result Inequalities of curvature measure imply Alexandrov curvature bounds.
We show that for every quasi-isometric map from a Hadamard manifold of pinched negative curvature to a locally compact, Gromov hyperbolic, CAT(0)-space there exists an energy minimizing harmonic map at finite distance. This harmonic map is moreover Lipschitz. This generalizes a recent result of Benoist-Hulin.
Harmonic maps from surfaces to CAT(k) spheres are branched coverings.
problem Uniformization of surfaces with CAT(k) metrics.
method Almost conformal harmonic maps and branched coverings.
result CAT(k) spheres are conformally equivalent to the 2-sphere.
The study improves harmonic map theory for metric spaces with curvature bounds.
problem Harmonic maps between specific metric spaces with curvature constraints.
method Synthetic geometry, Optimal Transport, Heat Flow, viscosity theory.
result Established Lipschitz continuity and Bochner-Eells-Sampson inequality.
New method glues Lorentzian spaces, preserving curvature bounds.
problem Creating new spaces from existing ones in Lorentzian geometry.
method Introducing an amalgamation process for Lorentzian pre-length spaces.
result Gluing preserves upper curvature bounds in spacetimes.
Busemann G-spaces with Finsler metrics
problem Admitting a differentiable DC atlas with a continuous Finsler metric
method Comparison geometry
result Generalizes previous work on G-spaces with Riemannian curvature bounds
The study proves a gap theorem for CAT(0) spaces with a constant below 1/(6√π).
problem Proving isoperimetric inequalities in non-positive curvature spaces.
method Introduced minimal tetrahedra to prove a linear inequality.
result Established a gap theorem for CAT(0) spaces with a constant below 1/(6√π).
The paper defines a new metric space invariant and computes it for various manifolds.
problem Computing the distributional LS-category of manifolds.
method Defining and analyzing the distributional LS-category of metric spaces and applying it to manifolds.
result Several sufficient conditions for the distributional LS-category of a closed manifold to be maximum are derived.
Study random walks on CAT(0) spaces with contracting elements, proving limit laws.
problem Analyzing random walks on spaces with non-positive curvature.
method Use of contracting elements and hyperbolic models for CAT(0) spaces.
result Prove almost sure convergence to the boundary without moment assumption.
Survey on harmonic maps in non-smooth spaces, focusing on rigidity.
problem Rigidity phenomena in non-smooth spaces.
method Regularity theory of harmonic maps to non-smooth targets.
result Generalizations of Margulis superrigidity and holomorphic rigidity of Teichmüller space.
Defines curvature for metric triples in metric spaces.
problem No standard curvature for metric triples in general metric spaces.
method Defines curvature kX(T) using side lengths and distances to points in X. result Curvature kX(T) enables isometric embedding into model spaces. Let Mk be the complete, simply connected, Riemannian 2-manifold of constant curvature k≤0. Let E be a closed, simply connected subspace of Mk with the property that every two points in E is connected by a rectifiable path in E. We show that under the induced path metric, E is a complete CAT(k) spa…
Proper proximality proved for various groups on non-positive curvature spaces.
problem Proper proximality of groups acting on non-positive curvature spaces.
method Established proper proximality for groups acting on CAT(0) spaces and hierarchically hyperbolic groups. result Proper proximality of many groups including mapping class groups and subgroups of curve graphs.
Study homology growth in nonpositive curvature spaces, finding examples of torsion.
problem Understanding homology growth in nonpositive curvature spaces.
method Computing mod p homology growth of right-angled Artin groups and closed locally CAT(0) manifolds.
result Homology torsion grows exponentially in the index of subgroups, contradicting rational homology growth.
First-passage percolation affects graph properties like curvature and geodesics.
problem Effect of first-passage percolation on graph curvature and geodesics.
method Randomly perturbs the metric of a graph by assigning random edge lengths.
result Non-positive curvature and geodesic properties are not preserved by first-passage percolation.
Geodesic currents in strongly hyperbolic spaces are dense.
problem Characterizing geodesic currents with strongly hyperbolic dual pseudometrics.
method Combining finite-cover argument and boundary data characterization.
result Dense subset of geodesic currents with strongly hyperbolic dual pseudometrics.
We extend the methods of Davis-Januszkiewicz-Lafont to provide a new obstruction to smooth Riemannian metric with non-positive sectional curvature. We construct examples of locally CAT(0) 4-manifolds M, whose universal covers satisfy isolated flats condition and contain 2-dimensional flats with the property that $\sq…
We show that if a noncollapsed CD(K,n) space X with n≥2 has curvature bounded above by κ in the sense of Alexandrov then K≤(n−1)κ and X is an Alexandrov space of curvature bounded below by K−κ(n−2). We also show that if a CD(K,n) space Y with finite n has curvature bounded above then it is inf…
We generalize the theory of gradient flows of semi-convex functions on CAT(0)-spaces, developed by Mayer and Ambrosio--Gigli--Savaré, to CAT(1)-spaces. The key tool is the so-called "commutativity" representing a Riemannian nature of the space, and all results hold true also for metric spaces satisfying the commutativi…
Study contractibility of boundaries in convex sets and limit sets of subgroups.
problem Understanding contractibility of boundaries and wildness of limit sets in geometric structures.
method Use sufficient conditions for contractibility, study coarse upper curvature bounds, and analyze interpolation in geodesic metric spaces.
result Conditions for contractibility of boundaries and properties of limit sets are established.
Researchers solve 3D cube complex boundary rigidity problem.
problem Determining the combinatorial type of a 3D CAT(0) cube complex from boundary distances.
method Discrete version of boundary rigidity problem, focusing on CAT(0) cube complexes.
result The combinatorial type of a finite CAT(0) cube complex can be reconstructed from its boundary distances.
Study of geometric actions on CAT(0) spaces and their limits.
problem Understanding limits of geometric actions on CAT(0) spaces.
method Analysis of convergence and splitting/collapsing phenomena in CAT(0) lattices and orbispaces.
result Proof of compactness theorem for CAT(0) homology orbifolds.
CAT(0) spaces with small volume growth are homeomorphic to Euclidean space.
problem Characterizing CAT(0) spaces with specific volume growth properties.
method Analyzing asymptotic topological regularity and volume growth.
result CAT(0) spaces with small volume growth are homeomorphic to Euclidean space.
Locally finite complexes with polyhedral CAT(0) metrics are arborescent.
problem Characterizing locally finite complexes with CAT(0) metrics. method Proving arborescence for complexes with polyhedral CAT(0) metrics. result Locally finite complexes with polyhedral CAT(0) metrics are arborescent. New CAT(0) groups show superexponential subgroup Dehn functions.
problem Understanding subgroups of CAT(0) groups with superexponential Dehn functions.
method Construction of specific 4- and 6-dimensional CAT(0) groups.
result Found subgroups with Dehn functions exp(n)(xm) and exp(n)(xα). We show that group actions on irreducible CAT(0) cube complexes with no free faces are uniquely determined by their ℓ1 length function. Actions are allowed to be non-proper and non-cocompact, as long as they are minimal and have no finite orbit in the visual boundary. This is, to our knowledge, the first …
Study distance maps on spaces with curvature bound, proving regularity and sphere theorem.
problem Regularity of distance maps on geodesically complete spaces with curvature bound above.
method Define and prove regularity of distance maps as Hurewicz fibrations.
result Sphere theorem for geodesically complete CAT(1) spaces.
CAT(0) study of curve complements and families.
problem Understanding CAT(0) behavior of curve complements and families.
method Investigation of fundamental groups of plane curve complements and universal families.
result Fundamental groups of certain families are not CAT(0).
We investigate the combinatorial and geometric properties of automorphism groups of universal right-angled Coxeter groups, which are the automorphism groups of free products of copies of Z_2. It is currently an open question as to whether or not these automorphism groups have non-positive curvature. Analogous to Outer …
Braid group proof shows 7-strand is CAT(0).
problem Proving the 7-strand braid group is CAT(0).
method Elaborating on Haettel, Kielak, and Schwer's argument.
result The 7-strand braid group is proven to be CAT(0).
Asymptotically CAT(0) metrics and Z-structures for HHGs, proving Farrell-Jones Conjecture.
problem Proving Farrell-Jones Conjecture for HHGs.
method Asymptotically CAT(0) metrics and Z-structures construction.
result Many HHGs satisfy Farrell-Jones Conjecture.
Toyoda proved 5-point CAT(0) spaces; this paper offers a new proof.
problem Describing 5-point subspaces in CAT(0) length spaces.
method Provides an alternative proof of Toyoda's theorem.
result Offers a new proof of Toyoda's theorem.
We show that groups satisfying Kazhdan's property (T) have no unbounded actions on finite dimensional CAT(0) cube complexes, and deduce that there is a locally CAT(-1) Riemannian manifold which is not homotopy equivalent to any finite dimensional, locally CAT(0) cube complex.
In this paper, we show a local energy convexity of W1,2 maps into CAT(K) spaces. This energy convexity allows us to extend Colding and Minicozzi's width-sweepout construction to produce closed geodesics in any closed Alexandrov space of curvature bounded from above, which also provides a generalized version of t…
Study mapping class groups on CAT(0) cube complexes.
problem Asymptotically rigid mapping class groups of infinitely-punctured surfaces.
method Introduced CAT(0) cube complexes and determined their properties.
result Determined CAT(0) properties of cube complexes.