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Questions on group theory which concern finite groups.

7 votes
3 answers
435 views

Subgroups of $GL(k,q)$ for bounded $k$

This question on subgroups of $GL(2,q)$ asked by Jan, and especially wonderful answers to it given by Geoff Robinson, Ralph, and Will Sawin showing that "almost no finite groups" inject in $GL(2,q)$ m …
Vladimir Dotsenko's user avatar
1 vote

Generate harmonic polynomials for a finite group

Maybe you need to be more clear about the word "similar". For example, the celebrated case of "diagonal harmonics" corresponding to the diagonal action of $S_n$ on $(\mathbb{C}^{2})^n$ there is some r …
Vladimir Dotsenko's user avatar
15 votes
Accepted

Reference for this theorem in representation theory?

I am not quite sure about the reference :( I always thought of this fact as follows. Matrix elements of tensor powers of a representation U are all possible monomials in matrix elements of U, so the …
Vladimir Dotsenko's user avatar
7 votes
1 answer
560 views

recognition of symmetric groups in GAP

In GAP (https://www.gap-system.org), there is a function IsSymmetricGroup, which tells you whether a subgroup of $S_n$ generated by given permutations is all of the $S_n$. It looks like it takes virtu …
Vladimir Dotsenko's user avatar
7 votes

factorization of the regular representation of the symmetric group

The fact that the Lie module (as proposed by Darij Grinberg) works, as well, as an explicit isomorphism of modules, follows from the theory of cyclic operads: see Corollary 6.9 in http://sites.math.no …
Vladimir Dotsenko's user avatar
3 votes

Isomorphisms $S^d(S^m(V)^*) \cong \Lambda^d(S^{m+d-1}(V)^*)$

If I remember correctly, one of the symmetric powers should become divided powers. A quick google search brought me to Section 3.4 of Aprodu, Farkas, Papadima, Raicu, and Weyman - Koszul modules and G …
Vladimir Dotsenko's user avatar
46 votes

Fun applications of representations of finite groups

An example from Kirillov's book on representation theory: write numbers 1,2,3,4,5,6 on the faces of a cube, and keep replacing (simultaneously) each number by the average of its neighbours. Describe ( …