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Questions about the branch of algebra that deals with groups.

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
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
5 votes
Accepted

Monolithic primitive groups without diagonals

You have left out a possbility for a monolithic action. It is possible to have $U\cap N=1$. This can occur when either S is abelian (here G is a subgroup of AGL(d,p) in its usual action on $p^d$ point …
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
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 …
Michael Giudici's user avatar
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
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
10 votes

Is $\varphi(n)/n$ the maximal portion of $n$-cycles in a degree $n$ group?

It is true for all primitive groups: The primitive groups of degree n containing an n-cycle were independently classified in Li, Cai Heng The finite primitive permutation groups containing an abelian …
Michael Giudici's user avatar
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 …
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
17 votes

Highly transitive groups (without assuming the classification of finite simple groups)

There is a classical result of Wielandt that if you assume the Schreier conjecture (that the outer automorphism group of an finite nonabelian simple groups is solvable), then a group of degree n other …
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

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