We point out that there are compact 4-manifolds which do not admit metrics of positive scalar curvature, but nonetheless have finite covering spaces which do carry such metrics. Moreover, passing from a 4-manifold to a covering space sometimes actually changes the sign of the Yamabe invariant. As was first pointed out by Bérard Bergery [1], there exist, in dimensions ≡ 1 or 2 mod 8, n ≥ 9, cert...

Spaces with radially symmetric curvature at base point p are shown to be diffeomorphic to space forms. Furthermore, they are either isometric to Rn or Sn under a radially symmetric metric, to RPn with Riemannian universal covering of Sn equipped with a radially symmetric metric, or else have constant curvature outside a metric ball of radius equal to the injectivity

If g(t) is a three-dimensional Ricci flow solution, with sectional curvatures that are O(t) and diameter that is O(t 1 2 ), then the pullback Ricci flow solution on the universal cover approaches a homogeneous expanding soliton.

We study the fundamental group of one–dimensional spaces. Among the results we prove are that the fundamental group of a second countable, connected, locally path connected, one–dimensional metric space is free if and only if it is countable if and only if the space has a universal cover and that the fundamental group of a compact, one–dimensional, connected metric space embeds in an inverse li...

We prove several structural results on definably compact groups G in o-minimal expansions of real closed fields such as (i) G is definably an almost direct product of a semisimple group and a commutative group, (ii) (G, ·) is elementarily equivalent to (G/G, ·). We also prove results on the internality of finite covers of G in an o-minimal environment, as well as deducing the full compact domin...

This work was partially supported by The Geometry Center of the University of Minnesota and the University of Massachusetts at Amherst. The soap film problem is to minimize area, and its dual is to maximize the flux of a divergenceless bounded vector field. This paper discretizes the continuous problem and solves it numerically. This gives upper and lower bounds on the area of the globally mini...

Let X be a finite aspherical CW-complex whose fundamental group π1(X) possesses a subnormal series π1(X) ⊲ Gm ⊲ . . . ⊲ G0 with a non-trivial elementary amenable group G0. We investigate the L2-invariants of the universal covering of such a CW-complex X. We show that the NovikovShubin invariants αn(X̃) are positive. We further prove that the L2-torsion ρ(2)(X̃) vanishes if π1(X) has semi-integral...

Berestovskii and Plaut introduced the concept of a coverable space [1] when developing their theory of generalized universal covering maps for uniform spaces. If a space is coverable and chain connected then it has a generalized universal covering map. Brodskiy, Dydak, LaBuz, and Mitra introduced the concept of a uniformly joinable space [2] when developing a theory of generalized uniform cover...

If G is a semidirect product N oH with N finitely generated then G has the property that every finite group is a quotient of some finite index subgroup of G if and only if one of N and H has this property. This has applications to 3-manifolds; for instance for any fibred hyperbolic 3-manifold M and any finite simple group S, there is a finite cyclic cover of M whose fundamental group surjects t...

The main theorem of this paper states that ifM is a closed orientable hyperbolic 3-manifold of volume at most 3.08, then the dimension of H1(M ;Z2) is at most 7, and that it is at most 6 unless M is “strange.” To say that a closed, orientable 3-manifold M , for which H1(M ;Z2) has dimension 7, is strange means that the Z2-vector space H1(M ;Z2) has a 2-dimensional subspace X such that for every...