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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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar
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{ …
Ali Taghavi's user avatar
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 …
Ali Taghavi's user avatar

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