We introduce an object which in a sense extends the notion of a covering space. Such an object is required to understand the “group” generated by the exponential functions of quadratic forms in the Weyl algebra, and gives in some sense a complexification of the metaplectic group.

We show that if a knot exterior satis"es certain conditions, then it has "nite cyclic coverings with arbitrarily large numbers of nontrivial algebraic components in their SL(2, ) character varieties (Theorem A). As an example, these conditions hold for hyperbolic punctured torus bundles over the circle (Theorem B). We investigate in more detail the "nite cyclic covers of the "gure-eight knot ex...

We write down the chain complex C∗ of the universal cover of the torus, and indicate how to do likewise for any 2-dimensional CW complex arising as the 2-skeleton of a K(G, 1). We exhibit a contracting chain homotopy for this chain complex, and again explain how to do so for the chain complex of the universal cover of our more general CW complex. This yields a contracting homotopy for the tenso...

We develop an explicit covering theory for complexes of groups, parallel to that developed for graphs of groups by Bass. Given a covering of developable complexes of groups, we construct the induced monomorphism of fundamental groups and isometry of universal covers. We characterize faithful complexes of groups and prove a conjugacy theorem for groups acting freely on polyhedral complexes. We a...

We study the existence of geometrically controlled branched covering maps from R to open 3-manifolds or to decomposition spaces S/G, and from S/G to S. Dedicated to the memory of Fred Gehring, whose work has been our inspiration

In this paper we define, for each aspherical orientable 3-manifold M endowed with a torus splitting T , a 2-dimensional fundamental l1-class [M ] whose l1norm has similar properties as the Gromov simplicial volume of M (additivity under torus splittings and isometry under finite covering maps). Next, we use the Gromov simplicial volume of M and the l1-norm of [M ] to give a complete characteriz...

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...

Let A be a closed subgroup of a connected, solvable Lie group G, such that the homogeneous space A\G is simply connected. As a special case of a theorem of C. T. C. Wall, it is known that every tessellation A\G/Γ of A\G is finitely covered by a compact homogeneous space G′/Γ′. We prove that the covering map can be taken to be very well behaved — a “crossed” affine map. This establishes a connec...

We notice that there is a 2-cover P of S 1 SO(3) (we denote this group D 1/2 ) by the group U(2): P sends a matrix z into a pair (det z,v). The matrix v here is the image of u under a standard covering map p from SU(2) onto SO(3), see (3.4) below. Finally, u (being a matrix from SU(2) ) is determined (up to a sign) from the decomposition z = du, here d 2 = det z. Both P and p are group homomorp...

We study the L-spectrum of the Laplace-Beltrami operator on certain complete locally symmetric spaces M = Γ\X with finite volume and arithmetic fundamental group Γ whose universal covering X is a symmetric space of non-compact type. We also show, how the obtained results for locally symmetric spaces can be generalized to manifolds with cusps of rank one.