F4 (Mathematics)

In mathematics, F4 is the name of a Lie group and also its Lie algebra \mathfrak{f}_4. It is one of the five exceptional simple Lie groups. F4 has rank 4 and dimension 52. Its center is the trivial subgroup. Its outer automorphism group is the trivial group. Its fundamental representation is 26-dimensional.

Algebra

The F4 Lie algebra may be constructed by adding 16 generators transforming as a spinor to the 36-dimensional Lie algebra so(9), in analogy with the construction of E8.

Dynkin diagram

Dynkin diagram of F_4

Roots of F4

(\pm 1,\pm 1,0,0)
(\pm 1,0,\pm 1,0)
(\pm 1,0,0,\pm 1)
(0,\pm 1,\pm 1,0)
(0,\pm 1,0,\pm 1)
(0,0,\pm 1,\pm 1)
(\pm 1,0,0,0)
(0,\pm 1,0,0)
(0,0,\pm 1,0)
(0,0,0,\pm 1)
(\pm\frac{1}{2},\pm\frac{1}{2},\pm\frac{1}{2},\pm\frac{1}{2})
Simple roots
(0,0,0,1)
(0,0,1,-1)
(0,1,-1,0)
(\frac{1}{2},-\frac{1}{2},-\frac{1}{2},-\frac{1}{2})

Weyl/Coxeter group

Its Weyl/Coxeter group is the symmetry group of the 24-cell.

Cartan matrix

\begin{pmatrix} 2&-1&0&0\\ -1&2&-2&0\\ 0&-1&2&-1\\ 0&0&-1&2 \end{pmatrix}

F4 lattice

The F4 lattice is a four dimensional body-centered cubic lattice (i.e. the union of two hypercubic lattices, each lying in the center of the other). They form a ring called the Hurwitz quaternion ring.

 

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