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Dec 12, 2015 at 17:04 comment added Kimball @DavidLoeffler Oh, do you mean to essentially look at the $SL_2(\mathbb Q)$ translates of a modular form? I guess this won't quite give you all of $\pi_f$, but a dense subset, which should be enough to get you Jacquet's global result, but it's not clear to me if you can translate his local analysis into this setting.
Dec 12, 2015 at 15:08 comment added Kimball @DavidLoeffler Ah, I didn't realize you could model $\pi_f$ classically. What does this classical model look like? And what does (upper half-plane)*($\widehat{\mathbb Z}^*$) mean?
Dec 12, 2015 at 10:14 comment added David Loeffler .. and unless I'm very much mistaken, the Petersson product of these Eisenstein series with vectors from (our model of) $\pi_f$ and $\pi'_f$ are exactly Jacquet's adelic integrals, so the GCD over all choices of the two cusp forms and the Schwartz function is (by definition) the $L$-function.
Dec 12, 2015 at 10:13 comment added David Loeffler ... The point is that test vectors at infinity are explicitly known, and one can write down the finite parts of the automorphic representations $\pi$ and $\pi'$ as explicit spaces of holomorphic functions on the upper half-plane (or more accurately on (upper half-plane) * ($\widehat{\mathbf{Z}}^*)$, to keep track of the component groups). One can also write down a collection of (non-holomorphic) Eisenstein series depending on a choice of a Schwartz function on $\mathbf{A}_f^2$;
Dec 12, 2015 at 10:11 comment added David Loeffler So you're basically saying that my question doesn't deserve to be answered because it's morally unsound? (Don't worry, I'm only joking! :-) ). But I think that some "middle way" between Jacquet's approach and the adelic approach does exist, and since posting my question I sat down and worked out the details.
Dec 11, 2015 at 16:58 history edited Jeremy Rouse CC BY-SA 3.0
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Dec 11, 2015 at 16:34 history answered Kimball CC BY-SA 3.0