4
votes
2answers
394 views
smallest simplest $E_8$ -module
What is the smallest simplest(non-trivial) $E_8$ -module ?
41
votes
3answers
2k views
Groups that do not exist
In the long process that resulted in the classification of finite simple groups, some of the exceptional groups were only shown to exist after people had computed (most of) their c …
12
votes
4answers
864 views
Triality of Spin(8)
Among simple Lie groups, $Spin(8)$ is the most symmetrical one in the sense that $Out(Spin(8))$ is the largest possible group. A description of this outer automorphism groups is as …
3
votes
3answers
321 views
Irreducibility of fundamental Weyl modules
It is known that for a simple algebraic group over an algebraically closed field of positive characteristic (which I assume to be {\it good} for the group), the Weyl modules corres …
1
vote
2answers
216 views
Is the derived group of $G_2$ simply connected?
I am interested in conjugacy classes in connected reductive groups over a non-archimedean field $F$ of characteristic $0$, or its algebraic closure. On this topic it is often requi …
23
votes
5answers
2k views
$G_2$ and Geometry
In a recent question Deane Yang mentioned the beautiful Riemannian geometry that comes up when looking at $G_2$. I am wondering if people could expand on the geometry related to th …
19
votes
6answers
902 views
Explanation for E_8’s torsion
To study the topology of Lie groups, you can decompose them into the simple compact ones, plus some additional steps, such as taking the cover if necessary. After that, the structu …
19
votes
2answers
1k views
Does $\mathrm{E}_7/(\mathrm{SU}_8/(\mathbb{Z}/2))$ carry an almost complex structure?
Recall the list of irreducible simply connected inner symmetric spaces of compact type in dimension $4k+2$:
Hermitian symmetric spaces (one can write them down explicitly);
Grass …
5
votes
1answer
492 views
Is there a connection between exceptional Galois groups and Ramanujan’s partition congruences
There are three exceptional Galois groups $L_2(5)$, $L_2(7)$ and $L_2(11)$ . These are cited as one of Arnold's "trinities" and are connected with other trinities and the McKay Cor …
5
votes
2answers
369 views
How do Jordan algebras help one understand representations of exceptional Lie algebras?
For this question I'm happy to take the complex numbers as the base field.
I've been trying to learn a little bit about the exceptional Lie algebras and for a while they seemed in …

