Thursday, 19 July 2007

rt.representation theory - Analogy between canonical basis of U(n_-) and Schur functors, each under restriction

.1. For any category mathcalC, possibly enriched over schemes, define Rep(mathcalC) to be the functor category mathcalCtobfVec with direct sum inherited from bfVec. (If mathcalC is enriched over schemes, like bfVec is since it's enriched over itself and vector spaces are schemes, then I probably only want functors that preserve this.) So it's easy to define irrep, etc. of mathcalC.



Fun fact: consider the irreps of bfVec, called the Schur functors. If we restrict them to reps of the single-object category (i.e. monoid) End(mathbbCn), some irreps restrict to 0, and the ones that don't go to 0 stay irreducible and give all the irreps of End(mathbbCn) exactly once! In standard indexing, the Schur functors correspond to partitions, the partitions with more than n rows restrict to 0, and the partitions with leqn rows give the irreps of End(mathbbCn).



.2. I am told that one of the nice properties of Lusztig's canonical basis B= { b } of U(mathfrakn) is that on any irrep V of G with high weight vector vecv, the nonzero bcdotvecv give a basis of V.



Is there a common framework for these two facts, perhaps involving categorifying the second one?



(I don't have anything riding on the answer... it's just a question I'd thought of a number of years ago and was reminded of by another mO question.)

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