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S. K. Roushon

Publications and source records attributed to S. K. Roushon.

At least 19 recordsLinked to original sources
arXiv2026

A four-term exact sequence of fundamental groups of orbit configuration spaces

We deduce that the fundamental groups of the orbit configuration spaces of an effective and properly discontinuous action of a discrete group on a connected aspherical 2-manifold, with isolated fixed points, fit into a four-term exact sequence. This comes as a consequence of the four-term exact sequence of orbifold pure braid groups ([18], [11] and [19]). The proof relates these two exact sequences and also draws a new consequence (Corollary 2.3) on the later one.

math.GT↗
arXiv2023

Orbifold braid groups

The orbifold braid groups of two dimensional orbifolds were defined in [1] (arXiv:math/9907194) to understand certain Artin groups as subgroups of some suitable orbifold braid groups. We studied orbifold braid groups in some more detail in [17] (arXiv:2006.07106) and [18] (arXiv:2106.08110), to prove the Farrell-Jones Isomorphism conjecture for orbifold braid groups and as a consequence for some Artin groups. In this article we apply the results from [17] and [18], to study two aspects of the orbifold braid groups. First we show that the homomorphisms induced on the orbifold braid groups by the inclusion maps of a generic class of sub-orbifolds of an orbifold are injective. Then, we prove that the centers of most of the orbifold braid groups are trivial.

math.GR↗
arXiv2023

Quasifibrations in configuration Lie groupoids and orbifold braid groups

In [19] we studied a Fadell-Neuwirth type fibration theorem for orbifolds, and gave a short exact sequence of fundamental groups of configuration Lie groupoids of Lie groupoids corresponding to the genus zero 2-dimensional orbifolds with cone points, and at least one puncture. In this paper we extend this work to all genus $\geq 1$, 2-dimensional orbifolds with cone points. As a consequence, we prove the Farrell-Jones Isomorphism conjecture for the fundamental groups of the associated configuration Lie groupoids. This answers a substantial part of a question we posed in [[18], Problem]. In [19] we also showed that for all global quotient type orbifolds, the fibration theorem does not hold. Here, we give some nontrivial examples of orbifolds where a Fadell-Neuwirth type quasifibration theorem holds. Finally, we state an Asphericity conjecture and a Quasifibration conjecture for orbifolds.

math.DG↗
arXiv2022

k-almost-quasifibrations

In [8](arXiv:2111.06159) we introduced the notion of a k-almost-quasifibration. In this article we update this definition and call it a k-c-quasifibration. This will help us to relate it to quasifibrations. We study some basic properties of k-c-quasifibrations. We also generalize a series of results on quasifibrations ([1]) to k-c-quasifibrations giving criteria for a map to be a k-c-quasifibration.

math.AT↗
arXiv2018

The isomorphism conjecture for Artin groups

We prove the Farrell-Jones fibered isomorphism conjecture for several classes of Artin groups of finite and affine types. As a consequence, we compute explicitly the surgery obstruction groups of the finite type pure Artin groups.

math.KT↗
arXiv2014

The isomorphism conjecture for groups with generalized free product structure

In this article we study the K- and L-theory of groups acting on trees. We consider the problem in the context of the fibered isomorphism conjecture of Farrell and Jones. We show that in the class of residually finite groups it is enough to prove the conjecture for finitely presented groups with one end. Also, we deduce that the conjecture is true for the fundamental groups of graphs of finite groups and of trees of virtually cyclic groups. To motivate the reader we include a survey on some classical works on this subject.

math.GT↗
arXiv2013

On the isomorphism conjecture for groups acting on trees

We study the Fibered Isomorphism conjecture of Farrell and Jones for groups acting on trees. We show that under certain conditions the conjecture is true for groups acting on trees when the stabilizers satisfy the conjecture. These conditions are satisfied in several cases of the conjecture. We prove some general results on the conjecture for the pseudoisotopy theory for groups acting on trees with residually finite vertex stabilizers. In particular, we study situations when the stabilizers belong to the following classes of groups: polycyclic groups, finitely generated nilpotent groups, closed surface groups, finitely generated abelian groups and virtually cyclic groups. Finally, we provide explicit examples of groups for which we have proved the conjecture in this article and show that these groups were not considered before. Furthermore, we deduce that these groups are neither hyperbolic nor CAT(0).

math.KT↗
arXiv2011

Vanishing structure set of 3-manifolds

In this short note we update a result proved in [16]. This will complete our program of [12] showing that the structure set vanishes for compact aspherical 3-manifolds.

math.GT↗
arXiv2010

Surgery on $\widetilde{\Bbb{SL}}\times\Bbb{E}^n$-manifolds

We show that although closed $\widetilde{\Bbb{SL}}\times\Bbb{E}^n$-manifolds do not admit metrics of nonpositive sectional curvature, the arguments of Farrell and Jones can be extended to show that such manifolds are topologically rigid, if $n\geq2$.

math.GT↗
arXiv2010

The isomorphism conjecture in L-theory: graphs of groups

We study the Fibered Isomorphism Conjecture of Farrell and Jones in L-theory for groups acting on trees. In several cases we prove the conjecture. This includes wreath products of abelian groups and free metabelian groups. We also deduce the conjecture in pseudoisotopy theory for these groups. Finally in B of Theorem 1.1 we prove the L-theory version of [[7], Theorem 1.2].

math.KT↗
arXiv2008

The isomorphism conjecture in L-theory

This is the first of three articles on the Fibered Isomorphism Conjecture of Farrell and Jones for L-theory. We apply the general techniques developed in [15] and [16] to the L-theory case of the conjecture and prove several results. Here we prove the conjecture, after inverting 2, for poly-free groups. In particular, it follows for braid groups. We also prove the conjecture for some classes of groups without inverting 2. In fact we consider a general class of groups satisfying certain conditions which includes the above groups and some other important classes of groups. We check that the properties we defined in [15] are satisfied in several instances of the conjecture.

math.KT↗
arXiv2007

The Borel conjecture for manifolds with virtually solvable fundamental groups

The article has been withdrawn by the author. Wolfgang Lueck and Peter Linnell pointed out that the proof of Lemma 3.8 does not apply to the unrestricted case of wreath product. It is not clear at this stage how to complete the proof of Theorem 3.1 using the present version of Lemma 3.8. The valid results originating from this article will be added in a later paper.

math.GT↗
arXiv2007

Algebraic K-theory of groups wreath product with finite groups

The Farrell-Jones Fibered Isomorphism Conjecture for the stable topological pseudoisotopy theory has been proved for several classes of groups. For example for discrete subgroups of Lie groups, virtually poly-infinite cyclic groups, Artin braid groups, a class of virtually poly-surface groups and virtually solvable linear group. We extend these results in the sense that if G is a group from the above classes then we prove the conjecture for the wreath product G with H for H a finite group. We also prove the conjecture for some other classes of groups.

math.KT↗
arXiv2006

The Farrell-Jones isomorphism conjecture for 3-manifold groups

We show that the Fibered Isomorphism Conjecture (FIC) of Farrell and Jones corresponding to the stable topological pseudoisotopy functor is true for the fundamental groups of a large class of 3-manifolds. We also prove that if the FIC is true for irreducible 3-manifold groups then it is true for all 3-manifold groups. In fact, this follows from a more general result we prove here, namely we show that if the FIC is true for each vertex group of a graph of groups with trivial edge groups then the FIC is true for the fundamental group of the graph of groups. This result is part of a program to prove FIC for the fundamental group of a graph of groups where all the vertex and edge groups satisfy FIC. A consequence of the first result gives a partial solution to a problem in the problem list of R. Kirby. We also deduce that the FIC is true for a class of virtually PD_3-groups. Another main aspect of this article is to prove the FIC for all Haken 3-manifold groups assuming that the FIC is true for B-groups. By definition a B-group contains a finite index subgroup isomorphic to the fundamental group of a compact irreducible 3-manifold with incompressible nonempty boundary so that each boundary component is of genus \geq 2. We also prove the FIC for a large class of B-groups and moreover, using a recent result of L.E. Jones we show that the surjective part of the FIC is true for any B-group.

math.KT↗
arXiv2006

The isomorphism conjecture for 3-manifold groups and K-theory of virtually poly-surface groups

This article has two purposes. In \cite{R3} (math.KT/0405211) we showed that the FIC (Fibered Isomorphism Conjecture for pseudoisotopy functor) for a particular class of 3-manifolds (we denoted this class by \cal C) is the key to prove the FIC for 3-manifold groups in general. And we proved the FIC for the fundamental groups of members of a subclass of \cal C. This result was obtained by showing that the double of any member of this subclass is either Seifert fibered or supports a nonpositively curved metric. In this article we prove that for any M in {\cal C} there is a closed 3-manifold P such that either P is Seifert fibered or is a nonpositively curved 3-manifold and π_1(M) is a subgroup of π_1(P). As a consequence this proves that the FIC is true for any B-group (see definition 3.2 in \cite{R3}). Therefore, the FIC is true for any Haken 3-manifold group and hence for any 3-manifold group (using the reduction theorem of \cite{R3}) provided we assume the Geometrization conjecture. The above result also proves the FIC for a class of 4-manifold groups (see \cite{R2}(math.GT/0209119)). The second aspect of this article is to relax a condition in the definition of strongly poly-surface group (\cite{R1} (math.GT/0209118)) and define a new class of groups (we call them {\it weak strongly poly-surface} groups). Then using the above result we prove the FIC for any virtually weak strongly poly-surface group. We also give a corrected proof of the main lemma of \cite{R1}.

math.KT↗