Abstract :
This paper explores properties of strictly imaginary roots of Kac-Moody algebras. (A strictly imaginary root is an imaginary root γ such that for any real root α either γ + α or γ − α is a root.) Its two major results are a simple test for whether or not a given imaginary root is strictly imaginary, and a complete characterization of those Kac-Moody algebras having the property that all of their imaginary roots are strictly imaginary.
