Thursday, 19 July 2007

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

.1. For any category mathcalCmathcalC, possibly enriched over schemes, define Rep(mathcalC)Rep(mathcalC) to be the functor category mathcalCtobfVecmathcalCtobfVec with direct sum inherited from bfVecbfVec. (If mathcalCmathcalC is enriched over schemes, like bfVecbfVec 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 mathcalCmathcalC.



Fun fact: consider the irreps of bfVecbfVec, called the Schur functors. If we restrict them to reps of the single-object category (i.e. monoid) End(mathbbCn)End(mathbbCn), some irreps restrict to 00, and the ones that don't go to 00 stay irreducible and give all the irreps of End(mathbbCn)End(mathbbCn) exactly once! In standard indexing, the Schur functors correspond to partitions, the partitions with more than nn rows restrict to 00, and the partitions with leqnleqn rows give the irreps of End(mathbbCn)End(mathbbCn).



.2. I am told that one of the nice properties of Lusztig's canonical basis B=B= { bb } of U(mathfrakn)U(mathfrakn) is that on any irrep VV of GG with high weight vector vecvvecv, the nonzero bcdotvecvbcdotvecv give a basis of VV.



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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