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Questions about the branch of algebra that deals with groups.

10 votes

Regular orbits for automorphisms of finite simple groups

By a result of Horoševskiĭ you can never find such an automorphism, that is all automorphisms of finite simple groups have a regular orbit.
Michael Giudici's user avatar
14 votes
Accepted

Does every transitive permutation group contain a permutation whose cycle lengths have a com...

There is a theorem of Fein, Kantor and Schacher that every finite transitive permutation group of degree at least two contains a derangement of prime power order, and hence all the cycle lengths are d …
Michael Giudici's user avatar
2 votes
Accepted

Inclusions among finite orthogonal groups over finite fields

The answer will depend on $q$, $\epsilon$ and potentially also $\ell$. Instead of looking at spinor norms you can find an element $x$ such that $\mathrm{SO}_2^\epsilon(q^\ell)=\langle \Omega_2^\epsilo …
Michael Giudici's user avatar
6 votes

Infinite vertex-transitive graph where every automorphism has a fixed vertex

Let $\Gamma$ be the graph whose vertices are the 2-dimensional subspaces of $\mathbb{R}^n$ and two will be adjacent if they intersect in a 1-dimensional subspace. Then $PGL(n, \mathbb{R})$ is in the a …
Michael Giudici's user avatar
6 votes

Generation of permutation groups by fixed elements subgroups

We looked at this question during our research retreat and obtained the following characterisation: If $H$ is transitive on $X$ then it will be generated by its point stabilisers if and only if it doe …
spin's user avatar
  • 2,821
5 votes
Accepted

describing embedding $U_3(q)<O_6^-(q)$, $q$ even

This is an example of a much more general embedding. Let $q$ be a prime power and $m$ a positive integer. Let $V$ be an $m$-dimensional vector space over $F=GF(q^2)$ and let $B:V\times V\rightarrow F$ …
Michael Giudici's user avatar
5 votes

Maximal subgroups of odd index in $\mathrm{PSL}(3,q)$

The maximal subgroups of odd index in finite simple groups were classified in Liebeck and Saxl - The primitive permutation groups of odd degree and independently in Kantor - Primitive permutation grou …
LSpice's user avatar
  • 12.9k
14 votes
Accepted

About the paper by Buekenhout, Delandtsheer, Doyen, Kleidman, Liebeck and Saxl

The proof for this appeared over a series of papers. The final one was Jan Saxl, `On Finite Linear Spaces with Almost Simple Flag-Transitive Automorphism Groups' Journal of Combinatorial Theory, Seri …
Emil Jeřábek's user avatar
13 votes

Maximal Sylow 2-subgroups of simple groups

Yes this follows from work of Baumann and Thompson. See the paper `On finite insoluble groups with nilpotent maximal subgroups' by John Rose https://doi.org/10.1016/0021-8693(77)90301-5 In fact, the …
Michael Giudici's user avatar
13 votes
Accepted

Have finite doubly transitive groups been classified?

The theorem of Aschbacher that is cited by Liebeck, looks at the maximal subgroups $G_0$ of a group $G$ satisfies $SL(a,p^{r/a})\leqslant G \leqslant \Gamma L(a,p^{(r/a})$. For the application of Lieb …
Michael Giudici's user avatar
20 votes

Can all the sporadic groups be expressed as permutation groups based on a single big cycle?

If a permutation group $G$ on a set of size $n$ contains an $n$-cycle then the subgroup $C$ generated by this $n$-cycle is transitive. Thus we have a factorisation $G=CG_\alpha$. Moreover, $C\cap G_\a …
Michael Giudici's user avatar
12 votes

fixed points of permutation groups

The Boston-Shalev Conjecture asserts that there is a constant $\delta$ such that for any transitive simple group $G$, the proportion of derangments in $G$ is at most $\delta$. After a long sequence of …
Michael Giudici's user avatar
8 votes
1 answer
1k views

Groups with an automorphism of order two fixing only two elements

It is well known that a finite group admitting an automorphism of order 2 that fixes only the identity is abelian and has odd order. Moreover, the automorphism is inversion. Is anything known about f …
13 votes
Accepted

polycirculant conjecture

The Conjecture is still open. Lemma 5 of math.GM/0204209 is false. For example, any primitive group on a prime number of points is a counterexample. Lemma 6 of math/0506617 is also false. Any trans …
Michael Giudici's user avatar
6 votes

Exact factorization of finite groups

The answer is no. $G=MN$ is an exact factorisation is equivalent to $N$ acting regularly on the set of right cosets of $M$ in $G$. It is not necessary for two regular subgroups of a group to be isomo …
Michael Giudici's user avatar

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