Affine action

Let $W$ be the Weyl group of a semisimple Lie algebra ${\mathfrak {g}}$ (associate to fixed choice of a Cartan subalgebra ${\mathfrak {h}}$). Assume that a set of simple roots in ${\mathfrak {h}}^{*}$ is chosen.

The affine action (also called the dot action) of the Weyl group on the space ${\mathfrak {h}}^{*}$ is

$w\cdot \lambda :=w(\lambda +\delta )-\delta$

where $\delta$ is the sum of all fundamental weights, or, equivalently, the half of the sum of all positive roots.

References

• Baston, Robert J.; Eastwood, Michael G. (1989), The Penrose Transform: its Interaction with Representation Theory, Oxford University Press.