On the fully commutative elements of type $\tilde C$ and faithfulness of related towers

Abstract

We define a tower of injections of $\tilde{C}$-type Coxeter groups $W(\tilde C_{n})$ for $n\geq 1$. We define a tower of Hecke algebras and we use the faithfulness at the Coxeter level to show that this last tower is a tower of injections. Let $W^c(\tilde C_{n})$ be the set of fully commutative elements in $W(\tilde C_{n})$, we classify the elements of $W^c(\tilde C_{n})$ and give a normal form for them. We use this normal form to define two injections from $W^c(\tilde C_{n-1})$ into $W^c(\tilde C_{n})$. We then define the tower of affine Temperley-Lieb algebras of type $\tilde{C }$ and use the injections above to prove the faithfulness of this tower.