# Questions tagged [gr.group-theory]

Questions about the branch of abstract algebra that deals with groups.

5,487 questions

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### Does every character from group factor through largest central subgroup?

Let $G$ be a coonected reductive algebraic group over $\mathbb{Q}$ and $A_G$ its largest $\mathbb{Q}$-split central torus over $\mathbb{Q}$.
Let $X(G)_{\mathbb{Q}}$ be the addtive group of ...

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### Simple One-relator Groups [on hold]

One-relator groups, that is, groups which admit a finite presentation $\langle A \: | \: w=1 \rangle$ for some $w \in A^\ast$, are well studied objects in combinatorial group theory. Many abstract ...

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### Open problems concerning all the finite groups

What are the open problems concerning all the finite groups?
The references will be appreciated. Here are two examples:
Aschbacher-Guralnick conjecture (AG1984 p.447): the number of conjugacy ...

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### Satake correspondence for groups over finite field

I asked the same question in MSE, but I didn't get any answer. So I decided to post it here, too.
In Langlands' program, Satake correspondence gives a correspondence between unramified ...

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### Meaning of epimorphism from full Galois group to some group

My problem has two parts: let $\;G:=Gal(\overline{\Bbb Q}/\Bbb Q)\;$ be the full Galois group of the rationals and $\;K\;$ be some finite group, then:
(1) Does having an epimorphism (of groups, in ...

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### What are the character tables of the finite unitary groups?

I need to know the (complex) character table of the finite unitary group $U_n(q)$. Lusztig and Srinivasan (1977) provide an abstract description, but parsing it requires a stronger background in ...

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### Bijection from $S^2$ to itself interchanging actions of $A_5$

Let $X$ and $Y$ be two copies of $S^2$, and let $A_5$ act on each of them (as a group of rotations). Call these actions $\theta_X$ and $\theta_Y$.
Moreover, let $g \in A_5$ be a fixed element of ...

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### Class of groups closed under “line supgroup”ing

Given a finitely generated group $H$, say that $G$ is a "line supgroup" of $H$ if $H < G$ (not necessarily normal), $G$ is finitely generated and for some set of generators of $G$, the Schreier ...

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### $\omega$-nilpotent cover of a recurrent surface

Theorem. Any $\omega$-nilpotent cover of a recurrent Riemannian manifold is Liouville.
$\omega$-nilpotent ($\Gamma=\bigcup_{i=1}^{\infty}Z_{i}$, $Z_{i}$ normal in $\Gamma$, where $Z_{n+1}$ maps to ...

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### Find representation set of orbits when group acts on a set

Let group $G$ acts on a set $S$. Burnside's lemma gives as how to count numbers of orbits. I am interested how to find the orbits. By finding orbits I mean how to find a representative from each orbit....

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### Which groups contain a comb?

The comb is the undirected simple graph with nodes
$\mathbb{N} \times \mathbb{N}$
where $\mathbb{N} \ni 0$ and edges
$$ \{\{(m,n), (m,n+1)\}, \{(m,0), (m+1,0)\} \;|\; m \in \mathbb{N}, n \in \mathbb{N}...

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### Uniform versus non-uniform group stability

Group stability considers the question of whether "almost"-homomorphisms are "close to" true homomorphisms. Here, "almost" and "close to" are made rigorous using a group metric.
More precisely, ...

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### On covers of groups by cosets

Suppose that ${\cal A}=\{a_sG_s\}_{s=1}^k$ is a cover of a group $G$ by (finitely many) left cosets with $a_tG_t$ irredundant (where $1\le t\le k$). Then the index $[G:G_t]$ is known to be finite. In ...

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### Conjugacy in metaplectic groups

Let $F$ be a non-Archimedean local field (characteristic 0) and $G=GL(2,F)$. Let $\tilde{G}$ be "the" metaplectic double cover of $G$ (defined using an explicit cocycle as in Gelbart's book (Weil's ...

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### Down to earth, intuition behind a Anabelian group [closed]

An anabelian group is a group that is “far from being an abelian group” in a precise sense: It is a non-trivial group for which every finite index subgroup has trivial center.
I would like to know ...