Extended affine root systems. I. Coxeter transformations

Extended Affine Root Systems

There are two notions of the extended affine root systems in the literature which both are introduced axiomatically. One, extended affine root system (SAERS for short), consists only of nonisotropic roots, while the other, extended affine root system (EARS for short), contains certain isotropic roots too. We show that there is a one to one correspondence between (reduced) SEARSs and EARSs. Name...

Root Systems and Coxeter Groups

This is a brief review of root systems and Coxeter groups, intended as background material for a course on double affine Hecke algebras and Macdonald polynomials. They are still incomplete in places. 1. Root systems Much of this material can be found in [Bou]. Let V be a real vector space with a positive definite inner product 〈·, ·〉. If α ∈ V is a non-zero vector, define the reflection sα in t...

Affine Permutations and an Affine Coxeter Monoid

In this expository paper, we describe results on pattern avoidance arising from the affine Catalan monoid. The schema of affine codes as canonical decompositions in conjunction with two-row moves is detailed, and then applied in studying the Catalan quotient of the 0-Hecke monoid. We prove a conjecture of Hanusa and Jones concerning periodicity in the number of fully-commutative affine permutat...

The Centroid of Extended Affine and Root Graded Lie Algebras

We develop general results on centroids of Lie algebras and apply them to determine the centroid of extended affine Lie algebras, loop-like and Kac-Moody Lie algebras, and Lie algebras graded by finite root systems.

Computational Aspects of Root Systems, Coxeter Groups, and Weyl Characters