10,352,975 research outputs found
Approximating L^2-signatures by their compact analogues
:Let G be a group together with an descending nested sequence of normal
subgroups G=G_0, G_1, G_2 G_3, ... of finite index [G:G_k] such the
intersection of the G_k-s is the trivial group. Let (X,Y) be a compact
4n-dimensional Poincare' pair and p: (\bar{X},\bar{Y}) \to (X,Y) be a
G-covering, i.e. normal covering with G as deck transformation group. We get
associated -coverings (X_k,Y_k) \to (X,Y). We prove that
sign^{(2)}(\bar{X},\bar{Y}) = lim_{k\to\infty} \frac{sign(X_k,Y_k)}{[G : G_k]},
where sign or sign^{(2)} is the signature or L^2-signature, respectively, and
the convergence of the right side for any such sequence (G_k)_k is part of the
statement
Maslov index, Lagrangians, Mapping Class Groups and TQFT
Given a mapping class f of an oriented surface Sigma and a lagrangian lambda
in the first homology of Sigma, we define an integer n_{lambda}(f). We use
n_{lambda}(f) (mod 4) to describe a universal central extension of the mapping
class group of Sigma as an index-four subgroup of the extension constructed
from the Maslov index of triples of lagrangian subspaces in the homology of the
surface. We give two descriptions of this subgroup. One is topological using
surgery, the other is homological and builds on work of Turaev and work of
Walker. Some applications to TQFT are discussed. They are based on the fact
that our construction allows one to precisely describe how the phase factors
that arise in the skein theory approach to TQFT-representations of the mapping
class group depend on the choice of a lagrangian on the surface.Comment: 31 pages, 11 Figures. to appear in Forum Mathematicu
Factor maps between tiling dynamical systems
We show that there is no Curtis-Hedlund-Lyndon Theorem for factor maps
between tiling dynamical systems: there are codes between such systems which
cannot be achieved by working within a finite window. By considering
1-dimensional tiling systems, which are the same as flows under functions on
subshifts with finite alphabets of symbols, we construct a `simple' code which
is not `local', a local code which is not simple, and a continuous code which
is neither local nor simple.Comment: 8 page
Stratified fibre bundles
A stratified bundle is a fibered space in which strata are classical bundles
and in which attachment of strata is controlled by a structure category of
fibers. Well known results on fibre bundles are shown to be true for stratified
bundles; namely the pull back theorem, the bundle theorem and the principal
bundle theorem.Comment: LaTeX file. Revised version. Accepted for publication on "Forum
Mathematicum
Manifolds associated with -colored regular graphs
In this article we describe a canonical way to expand a certain kind of
-colored regular graphs into closed -manifolds by
adding cells determined by the edge-colorings inductively. We show that every
closed combinatorial -manifold can be obtained in this way. When ,
we give simple equivalent conditions for a colored graph to admit an expansion.
In addition, we show that if a -colored regular graph
admits an -skeletal expansion, then it is realizable as the moment graph of
an -dimensional closed -manifold.Comment: 20 pages with 9 figures, in AMS-LaTex, v4 added a new section on
reconstructing a space with a -action for which its moment graph is
a given colored grap
The Lerch Zeta Function II. Analytic Continuation
This is the second of four papers that study algebraic and analytic
structures associated with the Lerch zeta function. In this paper we
analytically continue it as a function of three complex variables. We that it
is well defined as a multivalued function on the manifold M equal to C^3 with
the hyperplanes corresponding to integer values of the two variables a and c
removed. We show that it becomes single valued on the maximal abelian cover of
M. We compute the monodromy functions describing the multivalued nature of this
function on M, and determine various of their properties.Comment: 29 pages, 3 figures; v2 notation changes, homotopy action on lef
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