Saturday, 5 May 2007

rt.representation theory - Classification of finite complex reflection groups

Background:



Let $K$ be a field and let $V$ be a finite-dimensional $K$-vector space. A pseudoreflection (or usually imprecisely just reflection) in $V$ is an element $1 neq s in mathrm{GL}(V)$ fixing a hyperplane. A reflection representation of a group $W$ over $K$ is a $K$-linear representation $rho:W rightarrow mathrm{GL}(V)$, such that $rho(W)$ is generated by reflections. A group $W$ is called a reflection group over $K$ if it admits a reflection representation over $K$.



Shephard-Todd classified (see below) the finite irreducible reflection groups over $mathbb{C}$ (i.e. those finite groups admitting an irreducible reflection representation over $mathbb{C}$).



Question:



Is there also a classification of the finite irreducible reflection representations over $mathbb{C}$?



Edit: This question is very imprecise as indicated in the comments below. I should say what "classification of representations" means, and I have to admit: I don't know. A few ideas in this direction are:



  • determine the isomorphism classes of finite irreducible reflection representations over $mathbb{C}$, where an isomorphism between two reflection representations $rho:W rightarrow mathrm{GL}(V)$, $rho':W' rightarrow mathrm{GL}(V')$ is a vector space isomorphism $f:V rightarrow V'$ such that $f rho(G) f^{-1} = rho'(G)$. (I think the Shephard-Todd classification is a classification relative to this notion!?)


  • the same as above but an isomorphism is a vector space isomorphism $f:V rightarrow V'$ and a group isomorphism $varphi:W rightarrow W'$ such that $f rho(g) f^{-1} = rho'( varphi(g) )$ for all $g in W$.


  • consider pairs $(W,T)$ consisting of a finite irreducible reflection group over $mathbb{C}$ and a subset $T$ which are generating reflections of some irreducible reflection representation of $W$ and then determine isomorphism classes of such pairs.


  • [Insert your idea here].


My motivation for this question is something like this: A Cherednik-Algebra is defined for any finite irreducible reflection representation over $mathbb{C}$. In what sense does the algebra depend on the group alone and not on the choice of a particular reflection representation?

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