3
$\begingroup$

Is the representation of finite simple groups fully understood? To clarify, I mean have all the simple representations (even finite dimensional) been classified in terms of some classifying set, such as we have for simple Lie algebras/groups.

$\endgroup$
4
  • $\begingroup$ All irreducible representations of a finite group are finite-dimensional. I am fairly sure they have been classified for alternating and sporadic groups, but I don't know for the ones of Lie type. $\endgroup$ Commented Apr 25, 2021 at 13:45
  • 1
    $\begingroup$ Representation: over what kind of fields? algebraically closed? characteristic zero? $\endgroup$ Commented Apr 25, 2021 at 13:54
  • $\begingroup$ I guess over $\mathbb{R}$ and $\mathbb{C}$, but I would be interested to hear about finite fields as well. $\endgroup$ Commented Apr 25, 2021 at 14:16
  • $\begingroup$ I think the character tables over C for the sporadic groups are in the Atlas and there is a whole book by Carter I believe on the representation theory of the finite groups of Lie Type. I think the alternating groups is almost the same as the symmetric groups via Clifford theory. $\endgroup$ Commented Apr 25, 2021 at 14:25

1 Answer 1

7
$\begingroup$

A term that may fit in the scope of this problem is "generic character table", character tables of a whole family of groups of Lie type.

Example: Generic character table of $SL_2(q)$, $q = 2^f$

Representations $I$ $U$ $S(a)$ $T(b)$
Trivial $1$ $1$ $1$ $1$
Steinberg $q$ $0$ $1$ $-1$
Principal indexed by $k=1 \dots q/2 − 1$ $q+1$ $1$ $\epsilon^{ak}$$+$$\epsilon^{−ak}$ $0$
Discrete indexed by $l=1 \dots q/2$ $q-1$ $-1$ $0$ $−\eta^{bl}$$−$$\eta^{−bl}$

where $ \epsilon = \exp (2πi/(q − 1))$, $η = exp (2πi/(q + 1))$.

The generic character tables of the groups of Lie type $D_5(q)$ and $E_6(q)$ are still unknown, let alone $E_7(q)$ and $E_8(q)$.

And even if we worked out the whole character table, there is still a gap from the character table to representations. To see this, you can try to derive the representations from the character table above.

$\endgroup$
1
  • 3
    $\begingroup$ What does Deligne-Lusztig theory tell us about $D_5(q)$ and $E_6(q)$? $\endgroup$ Commented Apr 25, 2021 at 19:12

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.