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Any one know of any good references for reading about the Bernsteins Presentation of the Iwahori Hecke Algebra? I need some notes which has an example or two. It would really help.

edited Sep 28 2010 at 12:49

Johannes Hahn
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asked Sep 28 2010 at 12:29

unknown (google)
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Sheikraisinrollbank · Answer 1 · 2010-10-01 09:40:28Z UTC

In book form, the equivalence of the Coxeter and Bernstein presentations of the affine Hecke algebra appears in the first 4 chapters of Macdonald's book "Affine Hecke algebras and orthogonal polynomials". It is very carefully written, but the notation can get a bit heavy. When first reading it, I suggest you always assume that you are in case (1.4.1) in Macdonald's notation.

Chapter 6 does rank one examples.

Amritanshu Prasad · Answer 2 · 2010-10-01 04:09:43Z UTC

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I found the paper of Chriss and Khuri-Makdisi (Chriss, Neil; Khuri-Makdisi, Kamal. On the Iwahori-Hecke algebra of a $p$-adic group. Internat. Math. Res. Notices 1998, no. 2, 85--100.) quite helpful.

You may also look at Haines-Kottwitz-Prasad and Prasad.

answered Oct 1 2010 at 4:09

Amritanshu Prasad
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	Dear Amri, Kottwitz once gave me a short set of notes (4 pages, I think) about Bernstein's presentation (maybe for split groups?), which I found very helpful. Did you ever see those? Do you know if they ever appeared somewhere (or are available online)? – Emerton Oct 1 2010 at 5:45
	He gave some lectures on Iwahori-Hecke algebras in 2000 or 2001. The notes for those lectures were [hugely] expanded into our paper by Tom. Maybe the notes that you are talking of were the original notes for those lectures? I do not know of anything else that got published. Tom is probably a better person to ask. – Amritanshu Prasad Oct 1 2010 at 10:09

Jim Humphreys · Answer 3 · 2010-09-28 15:52:42Z UTC

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Like some of his other important ideas, Bernstein's presentation has mostly been disseminated through the papers of other people. Probably the most influential is the 1989 JAMS paper by Lusztig, freely available from the AMS here. Combinatorial work by Arun Ram and others involving affine Hecke algebras also depends on this viewpoint: see for example Parkinson-Ram

Two relevant recent papers with extensive references are also available on arXiv and would be worth looking at in any case: haines-pettit and goertz.

edited Sep 28 2010 at 15:52

answered Sep 28 2010 at 15:23

Jim Humphreys
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Do you know of a reference that treats the nonsplit case as well? Even the case of a quasisplit group that splits over an unramified extension (a so-called "unramified group" by some) would be helpful to me. – Marty Sep 28 2010 at 16:27

Marty: The short answer is no. My knowledge of *p*-adic groups and such is fairly superficial. The older work of Iwahori-Matsumoto on "Hecke" algebras involved just split groups, but since then the subject has been developed (by a lot of people) far beyond my attention span. – Jim Humphreys Sep 28 2010 at 17:53

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Marty: Lusztig sets everything up to work in the non-split case. (Would you expect anything less?) He does not mention algebraic groups in the JAMS article, and so in order to connect his algebra to an algebraic group, you'd have to dig through Bruhat-Tits. For the unramified case, that digging is (as you probably know) not too painful. – james-parson Sep 29 2010 at 3:03

Yes, the affine Hecke algebra is not tied directly to a specific application though it was originally studied in the context of split $p$ -adic groups (where the affine Weyl group can replace the finite Weyl group to give an interesting BN-pair structure in the algebraic group). – Jim Humphreys Sep 29 2010 at 17:46

@Marty: I think if you look at Lusztig's second paper on unipotent representations of p-adic groups he discusses the unramified case, possibly quite tersely, but it might be worth a look. – Kevin McGerty Oct 1 2010 at 9:19

Bugs Bunny · Answer 4 · 2010-09-28 19:49:44Z UTC

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MathSciNet search for Hecke and Bernstein Presentation gives this ...

edited Sep 28 2010 at 19:49

answered Sep 28 2010 at 14:02

Bugs Bunny
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Bernstein’s presentation for the Hecke Algebra

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