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5 votes
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Recursive formula for inverse Kazhdan-Lusztig polynomials

The case of an affine Weyl group is apparently the only one which has been looked at closely. But it may be hard to answer your specific question. As far as I know, there are two relevant papers, …
Jim Humphreys's user avatar
7 votes

Examples of non-trivial Kazhdan-Lusztig polynomials

Already in the case of finite symmetric groups, one can find any polynomial with non-negative integral coefficients and constant term 1 as KL polynomial for some pair of group elements. See the pa …
Jim Humphreys's user avatar
2 votes
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Kazhdan–Lusztig polynomials in terms of Ext groups

The answer is yes, for fairly elementary reasons, though it's not easy to give a reference. The point is partly that the polynomials are undefined for two elements of the Weyl group not related by t …
Jim Humphreys's user avatar
11 votes

Subquotients in the Verma filtration on Verma modules

Contrary to Verma's initial impression, the internal structure of a "Verma module" (Dixmier's terminology) tends to be extremely complicated. However, this complexity only shows up in ranks 3 or hig …
Jim Humphreys's user avatar
3 votes

Around the socle filtration of a Verma module

Concerning the basic question (a), my first reaction is to be skeptical. Though as you say miracles sometimes do occur in this subject. I don't have a counterexample at my fingertips. Beyond the …
Jim Humphreys's user avatar
2 votes

Is there a list of Kazhdan-lusztig polynomials?

Here are some cautionary remarks, plus references. You ask: Is there a more comprehensive list of such polynomials? The answer seems to be no. Lists get long very quickly, and as I commented ea …
Jim Humphreys's user avatar
3 votes

Implications of non-negativity of coefficients of arbitrary Kazhdan-Lusztig polynomials?

Maybe I can provide a belated kind of answer to my own question, which I came across when looking for something else in the older literature. Vinay Deodhar published a paper in 1990 here (just before …
Jim Humphreys's user avatar
41 votes
2 answers
2k views

Implications of non-negativity of coefficients of arbitrary Kazhdan-Lusztig polynomials?

In their seminal 1979 paper Representations of Coxeter groups and Hecke algebras (Invent. Math. 53, doi:10.1007/BF01390031), Kazhdan and Lusztig studied an arbitrary Coxeter group $(W,S)$ and the corr …
Jim Humphreys's user avatar