scholarly journals Milnor excision for motivic spectra

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Elden Elmanto ◽  
Marc Hoyois ◽  
Ryomei Iwasa ◽  
Shane Kelly
Keyword(s):  
Cohomological Dimension ◽  
Commutative Rings ◽  
Cohomology Theory ◽  
Virtual Cohomological Dimension

Abstract We prove that the ∞ {\infty} -category of motivic spectra satisfies Milnor excision: if A → B {A\to B} is a morphism of commutative rings sending an ideal I ⊂ A {I\subset A} isomorphically onto an ideal of B, then a motivic spectrum over A is equivalent to a pair of motivic spectra over B and A / I {A/I} that are identified over B / I ⁢ B {B/IB} . Consequently, any cohomology theory represented by a motivic spectrum satisfies Milnor excision. We also prove Milnor excision for Ayoub’s étale motives over schemes of finite virtual cohomological dimension.

scholarly journals Presentability by products for some classes of groups

2017 ◽  
Vol 09 (01) ◽  
pp. 27-49
Author(s):  
P. de la Harpe ◽  
D. Kotschick
Keyword(s):  
Coxeter Groups ◽  
Cohomological Dimension ◽  
Fundamental Groups ◽  
Finitely Generated ◽  
Infinite Groups ◽  
Finitely Generated Groups ◽  
Dense Subgroups ◽  
Finite Index Subgroups ◽  
Virtual Cohomological Dimension ◽  
By Products

In various classes of infinite groups, we identify groups that are presentable by products, i.e. groups having finite index subgroups which are quotients of products of two commuting infinite subgroups. The classes we discuss here include groups of small virtual cohomological dimension and irreducible Zariski dense subgroups of appropriate algebraic groups. This leads to applications to groups of positive deficiency, to fundamental groups of three-manifolds and to Coxeter groups. For finitely generated groups presentable by products we discuss the problem of whether the factors in a presentation by products may be chosen to be finitely generated.

ON GROUPS OF TYPE $\mathcal{L}^{-1}$

2010 ◽  
Vol 21 (06) ◽  
pp. 727-736
Author(s):  
JANG HYUN JO
Keyword(s):  
Finite Group ◽  
Algebraic Property ◽  
Cohomological Dimension ◽  
Finite Dimensional ◽  
Free Actions ◽  
Virtual Cohomological Dimension ◽  
Algebraic Counterpart

We show that every finite group G has a set of cohomological elements satisfying ceratin algebraic property [Formula: see text] which can be regarded as a generalized notion of an algebraic counterpart to the topological phenomenon of free actions on finite dimensional homotopy spheres. We extend this result to a certain class of groups which contains groups of finite virtual cohomological dimension.

BOUNDARY OF CAT(-1) COXETER GROUPS

1999 ◽  
Vol 09 (02) ◽  
pp. 169-178 ◽  
Author(s):  
N. BENAKLI
Keyword(s):  
Coxeter Groups ◽  
Cohomological Dimension ◽  
Existence Problem ◽  
Joint Work ◽  
Coxeter Graph ◽  
Combinatorial Properties ◽  
Jsj Decomposition ◽  
Complete Bipartite Graphs ◽  
Dimension 2 ◽  
Virtual Cohomological Dimension

In this paper, we study the topological properties of the hyperbolic boundaries of CAT(-1) Coxeter groups of virtual cohomological dimension 2. We will show how these properties are related to combinatorial properties of the associated Coxeter graph. More precisely, we investigate the connectedness, the local connectedness and the existence problem of local cut points. In the appendix, in a joint work with Z. Sela, we will construct the JSJ decomposition of the Coxeter groups for which the corresponding Coxeter graphs are complete bipartite graphs.

scholarly journals Trace forms of G-Galois algebras in virtual cohomological dimension 1 and 2

2004 ◽  
Vol 217 (1) ◽  
pp. 29-43 ◽  
Author(s):  
Eva Bayer-Fluckiger ◽  
Marina Monsurrò ◽  
R. Parimala ◽  
René Schoof
Keyword(s):  
Cohomological Dimension ◽  
Trace Forms ◽  
Virtual Cohomological Dimension

Farrell cohomology and centralizets of elementary abelian p-subgroups

1996 ◽  
Vol 119 (3) ◽  
pp. 403-417 ◽  
Author(s):  
Chun-Nip Lee
Keyword(s):  
Finite Groups ◽  
Automorphism Groups ◽  
Outer Automorphism ◽  
Cohomological Dimension ◽  
Finite Graph ◽  
Mapping Class ◽  
Torsion Free Subgroup ◽  
Outer Automorphism Groups ◽  
Virtual Cohomological Dimension ◽  
Torsion Free

Let Γ be a discrete group. Γ is said to have finite virtual cohomological dimension (vcd) if there exists a finite index torsion-free subgroup Γ′ of G such that Γ′ has finite cohomological dimension over ℤ. Examples of such groups include finite groups, fundamental group of a finite graph of finite groups, arithmetic groups, mapping class groups and outer automorphism groups of free groups. One of the fundamental problems in topology is to understand the cohomology of these finite vcd-groups.

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