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Apr 17, 2023 at 12:51 comment added Maty Mangoo I think it is better if you leave the answer. I now added a little more to my already overloaded content by trying to explain in more detail what I wish to obtain.
Apr 15, 2023 at 23:14 comment added David Loeffler I see. So it looks like you were actually asking a different and more subtle question from the one I answered – apologies for jumping to conclusions! Do you want me to delete this answer? That might increase the chances of a real expert coming along and answering your actual question.
Apr 15, 2023 at 18:13 comment added Maty Mangoo Bump and co. calls this operator in the recursion a modified Kazdhan-Lusztig operator. What I would be interested in is understand this transition by means of rep.theory.
Apr 15, 2023 at 18:09 comment added Maty Mangoo while it is true that (at least for the long Weyl-element), the (Iwahori-spherical) Whittaker function restricted to the diagonal torus has the form you stated, its values on $\pi^e \cdot w$ are not so easy to describe. In deed, if one sticks to $n=2$, then for example for $w = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$ one gets $$ \mathcal{W}(\pi^e w) = (\delta^{1/2}_2 \otimes \tau^{w})(\pi^{e}) \cdot \left(\frac{1 - q^{-1} + q^{-1}\left(\frac{\alpha}{\beta}\right)^{e_2-e_1 + 2} - \left(\frac{\alpha}{\beta}\right)^{e_2-e_1 + 1}}{1 - \frac{\alpha}{\beta}}\right). $$
Apr 15, 2023 at 16:48 history answered David Loeffler CC BY-SA 4.0