§ Mnemonic for Specht module actions
Consider the two extreme cases, of wide v/s narrow:
x = [* * *]
y = [#]
[#]
[#]
- Consider
x = [* * *]
. It's very wide/fat, so it doesn't like much exercise, which is why it's columns stabilizer Cx={e} is trivial. Thus, the action Ax≡id.
- Consider
y = [*][*][*]
. It's very slim, and exercises quite a bit. So it's column stabilizer is S3, and its action Ay≡… has a lot of exercise.
- Anyone can participate in x's exercise regime. In particular, Ax(y)=id(y)=y since y doesn't tire out from the exercise regime of x.
- On the other side, it's hard to take part in y's exercise regime and not get TODOed out. If we consider Ay(x), we're going to get zero because by tableaux, there are swaps in Ay that leave x invariant, which causes sign cancellations. But intuitively, Ay(x) is asking xto participate in y's exercise regmine, which it's not strong enough to do, and so it dies.
- In general, if λ▹μ, then λ is wider/fatter than μ. Thus we will have Aμ(λ)=0 since Aμ is a harder exercise regime that has more permutations.
- Extend this to arrive at specht module morphism: If we have a non-zero morphism ϕ:Sλ→Sμ then λ→μ [Check this?? Unsure ]