If X is a geodesic metric space and x1, x2, x3 ∈ X, a geodesic triangle T = {x1, x2, x3} is the union of the three geodesics [x1x2], [x2x3] and [x3x1] in X. The space X is δ-hyperbolic (in the Gromov sense) if any side of T is contained in a δ-neighborhood of the union of the two other sides, for every geodesic triangle T in X. We denote by δ(X) the sharp hyperbolicity constant of X, i.e., δ(X)...

A geodesic metric space X is called hyperbolic if there exists δ ≥ 0 such that every geodesic triangle ∆ in X is δ-slim, i.e., each side of ∆ is contained in a closed δ-neighborhood of the two other sides. Let G be a group generated by a finite set A and let Γ(G,A) be the corresponding Cayley graph. The group G is said to be word hyperbolic if Γ(G,A) is a hyperbolic metric space. A subset Q of ...

Schultz (2018) generalized the work of Rajala and Sturm (2014), proving that a weak non-branching condition holds in more general setting very strict CD spaces. Anyway, similar to what happens for strong condition, seems not be stable with respect measured Gromov Hausdorff convergence (cf. Magnabosco, 2022). In this article I prove stability result assuming some metric requirements on convergin...

In this article we study Sobolev metrics of order one on diffeomorphism groups on the real line. We prove that the space Diff1(R) equipped with the homogenous Sobolev metric of order one is a flat space in the sense of Riemannian geometry, as it is isometric to an open subset of a mapping space equipped with the flat L2-metric. Here Diff1(R) denotes the extension of the group of all either comp...

Let S be a set of n points and let w be a function that assigns non-negative weights to points in S. The additive weighted distance dw(p, q) between two points p, q ∈ S is defined as w(p) + d(p, q) + w(q) if p 6= q and it is zero if p = q. Here, d(p, q) denotes the (geodesic) Euclidean distance between p and q. A graph G(S,E) is called a t-spanner for the additive weighted set S of points if fo...

Let l be a length function on a group G, and let Ml denote the operator of pointwise multiplication by l on l(G). Following Connes, Ml can be used as a “Dirac” operator for C ∗ r (G). It defines a Lipschitz seminorm on C∗ r (G), which defines a metric on the state space of C∗ r (G). We investigate whether the topology from this metric coincides with the weak-∗ topology (our definition of a “com...

In this article we exhibit the largest constant in a quadratic isoperimetric inequality which ensures that a geodesic metric space is Gromov hyperbolic. As a particular consequence we obtain that Euclidean space is a borderline case for Gromov hyperbolicity in terms of the isoperimetric function. We prove similar results for the linear filling radius inequality. Our theorems strengthen and gene...

On any compact Kähler manifold, Mabuchi [16], Semmes [17], and Donaldson [5] introduced a Weil-Peterson type metric in the space of Kähler metrics and proved that it is a formally non-positively curved symmetric space of “noncompact” type. According to [17], the geodesic equation can be transformed into a homogenous complex Monge-Ampere equation. In [5], Donaldson proposed an ambitious program ...

The topology and geometry of the moduli space, M2, of degree 2 static solutions of the CP 1 model on a torus (spacetime T 2 × R) are studied. It is proved that M2 is homeomorphic to the left coset space G/G0 where G is a certain eight-dimensional noncompact Lie group and G0 is a discrete subgroup of order 4. Low energy two-lump dynamics is approximated by geodesic motion on M2 with respect to a...

This paper presents a novel approach based on the shape space concept to classify deformations of 3D models. A new quasi-conformal metric is introduced which measures the curvature changes at each vertex of each pose during the deformation. The shapes with similar deformation patterns follow a similar deformation curve in shape space. Energy functional of the deformation curve is minimized to c...