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Questions about the branch of algebra that deals with groups.
15
votes
0
answers
715
views
Is this "Homology" useful to study?
In the usual singular homology of a topological space $X$, one consider the free abelian group generated by all continuous maps from the standard simplex $\Delta^{n}$ to $X$.
Now we can r …
15
votes
1
answer
782
views
The completion of the space of finite groups
Edit: I revise the question based on the comment conversations
Let $\mathcal{F}$ be the set of all equivalence classes of finite groups under the "Isomorphism" equivalence relation.
We define …
9
votes
2
answers
664
views
Semi group of polynomials which all roots lie on the unit circle
Let $X=\{f\in \mathbb{C}[z]\mid |z| \neq 1 \implies f(z) \neq 0\} $.
The motivation for consideration of such an $X$ is the the concept of Lee-Yang polynomials.
With the standard multiplication, $X …
8
votes
1
answer
619
views
Why is this group called "The Holomorph of a group"
Many years ago I found in google the notation "Holomorph of group". It is the semi direct product of $G$ with $Aut(G)$. Why is the term "Holomorph" used here, while it is usually used for complex anal …
7
votes
1
answer
475
views
How can one define a kind of "determinant" on a reduced group $C^*$ algebra?
Let $A$ be a unital $C^*$-algebra which is equipped with a faithful trace $T$. In particular we may consider $A=C^*_{\text{red}} (G)$ for some discrete group $G$. We consider the following differentia …
6
votes
2
answers
447
views
A possible characterization of the category of finite $p$-groups
Let $\mathcal{FG}$ be the category of finite groups. Let $S$ be a full subcategory of $\mathcal{FG}$.
Assume that $G\in \mathcal{FG}$ and $P\in S$ is a subgroup of $G$. We say that $P$ is $S$-maximal …
6
votes
1
answer
250
views
Is $G\mapsto \operatorname{Hol}(G)$ the object component of any functor on the category of g...
On the objects of the category of groups we define the mapping $G\mapsto \operatorname{Hol}(G)$, the holomorph $G\rtimes \operatorname{Aut}(G)$ of $G$. Can we extend this mapping to a functor on this …
5
votes
0
answers
208
views
Divisible orientation preserving diffeomorphism which is time-$1$ map of no smooth flow
Is there an orientation preserving smooth diffeomorphism $f$ on a compact manifold $M$ such that
for every $n\in \mathbb{N}$, there is a smooth diffeomorphism $g:M \to M$, as $n$th root of …
5
votes
2
answers
494
views
Is every countable discrete group a subgroup of a non discrete Lie group?
1)Let $G$ be a countable discrete group. Can $G$ be embbeded in a locally connected Lie group?
2)let $G$ be a countable discrete group with a prescribed generating set and corresponding word metr …
5
votes
1
answer
303
views
Amenability of $S^{\infty}$
Let $G$ be the group of all permutations of $\mathbb{N}$. If I am not mistaken, this group is denoted by $S^{\infty}$.
Is there a precise locally compact topology on $G$ such that $G$ would b …
5
votes
1
answer
613
views
Can the full and reduced group $C^*$-algebras be "noncanonically" isomorphic?
Is there a locally compact group $G$ such that the canonical map from $C^{*}(G)$ to $C^{*}_{red} G$ is not isomorphism, hence $G$ is not amenable but these two $C^{*}$ algebras are isomorphic …
4
votes
1
answer
409
views
Functors on the category of abelian groups which satisfy $F(G\times H) \cong F(G)\otimes_{\m...
Edit: According to the comment of Todd Trimble, I revise the question.
What are some examples of functors $F$ on the category of Abelian groups or category of rings which satisfy $$F(G\times H)\cong …
4
votes
1
answer
199
views
Groups for which all projections of $C^*_{\text{red}}G$ belong to $\mathbb{C}G$
Revision: According to comment of Wojowu we give a complete revise for this post.
A group $G$ is a pr-group if all projections of $C^*_{\text{red}} G$ are contained in its dense subalgebra $\mathbb{ …
3
votes
Solving algebraic problems with topology
The following paper and its references contains some algebraic consequences of vector bundle theory.
Vakhtang Lomadze, Applications of vector bundles to factorization of rational matrices, Line …
3
votes
0
answers
105
views
A generalization of the character group
Let $G$ be a group.
We define $$\tilde{G}=\{\phi:G \to \mathbb{T}\mid \phi(gh){\phi(g)}^{-1}{\phi(h)}^{-1}\in Tor(\mathbb{T})\}$$
where $Tor(\mathbb{T})$ is the group of torsion elements of the unit c …