5 ,
1 ,
1 ,
1
The Hecke algebra for the Symmetric Group
on 8 Letters, with the Partition
[ 5, 1, 1, 1 ]
in characteristic 5
.
The Module M
The module M is the permutation module over the prime
field of chacteristic 5, having point stablilizer
equal to the Young subgroup of the partition.
The dimension of M is 336
.
The dimensions of the irreducible submodules modules are
43,
35,
21,
21,
20,
7,
1
.
The module M has radical filtration (Loewy series)
2,
3,
3,
3,
5,
5,
5,
6,
6,
6,
7
1,
1,
4
3,
3,
6
The module M has socle filtration (socle series)
3,
3,
6
1,
1,
4
2,
3,
3,
3,
5,
5,
5,
6,
6,
6,
7
The module M has simple direct summands:
1 copy of simple module number 2
1 copy of simple module number 3
3 copies of simple module number 5
2 copies of simple module number 6
1 copy of simple module number 7
The remaining indecomposable components of M
have radical and socle filtrations as follows:
1).
radical layers
3
1
3
socle layers
3
1
3
2).
radical layers
3
1
3
socle layers
3
1
3
3).
radical layers
6
4
6
socle layers
6
4
6
The Action Algebra
The action algebra A is the image of kG in the
k-endomorphism ring of M. It's simple modules are the irreducible
submodules of M.
The dimensions of the projective modules are
64,
35,
85,
28,
20,
35,
1
.
The cartan matrix of A is
1,
0,
1,
0,
0,
0,
0
0,
1,
0,
0,
0,
0,
0
1,
0,
2,
0,
0,
0,
0
0,
0,
0,
1,
0,
1,
0
0,
0,
0,
0,
1,
0,
0
0,
0,
0,
1,
0,
2,
0
0,
0,
0,
0,
0,
0,
1
The determinant of the Cartan matrix is 1.
The blocks of A consist of the following irreducible
modules:
(1).
1,
3
(2).
2
(3).
4,
6
(4).
5
(5).
7
Projective modules number
2,
5,
7
are simple.
The radical and socle filtrations of the remaining
projective modules for A are the following:
Projective module number 1
radical layers
1
3
socle layers
1
3
Projective module number 3
radical layers
3
1
3
socle layers
3
1
3
Projective module number 4
radical layers
4
6
socle layers
4
6
Projective module number 6
radical layers
6
4
6
socle layers
6
4
6
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1
.
The Hecke Algebra
The Hecke algebra H of the module M is the A-endomorphism
ring of M.
The dimension of H is
34
.
The dimensions of the irreducible H-modules are
3,
2,
2,
1,
1,
1,
1
.
The degrees of the splitting fields are
1,
1,
1,
1,
1,
1,
1
.
The dimensions of the projective modules of H are
3,
3,
5,
1,
1,
3,
4
.
The cartan matrix of H is
1,
0,
0,
0,
0,
0,
0
0,
1,
0,
0,
0,
0,
1
0,
0,
2,
0,
0,
1,
0
0,
0,
0,
1,
0,
0,
0
0,
0,
0,
0,
1,
0,
0
0,
0,
1,
0,
0,
1,
0
0,
1,
0,
0,
0,
0,
2
The determinant of the Cartan matrix is 1.
The blocks of H consist of the following irreducible
modules:
(1).
1
(2).
2,
7
(3).
3,
6
(4).
4
(5).
5
Projective modules number
1,
4,
5
are simple.
The radical and socle filtrations of the remaining
projective modules for H are the following:
Projective module number 2
radical layers
2
7
socle layers
2
7
Projective module number 3
radical layers
3
6
3
socle layers
3
6
3
Projective module number 6
radical layers
6
3
socle layers
6
3
Projective module number 7
radical layers
7
2
7
socle layers
7
2
7