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Sep 17, 2019 at 14:53 comment added David Loeffler Agreed, but twisting by a Dirichlet char will change the $\epsilon$-factor.
Sep 17, 2019 at 12:29 comment added Peter Humphries With that being said, the $L$-function of a self-dual Gelbart-Jacquet lift $\Pi$ whose epsilon factor satisfies $\epsilon(1/2,\Pi) = -1$ trivially vanishes at $s = 1/2$.
Sep 17, 2019 at 9:02 comment added David Loeffler Certainly it is expected that for any cuspidal auto $\pi$ on $GL(3)$, and any finite set of places $S$, we have $L(\pi, \chi, 1/2) \ne 0$ for all but finitely many finite-order characters $\chi$ unram outside $S$; but I don't think this is known (whether or not $\pi$ is a GJ lift).
Sep 17, 2019 at 7:09 comment added Damon Thanks a lot for these clarifications. Even if the epsilon factor is nonzero, can we have L-value zero at 1/2? Is that possible for instance for all characters ?
Sep 15, 2019 at 16:32 comment added Peter Humphries For what it's worth, I've found Gelbart and Jacquet's paper (doi.org/10.24033/asens.1355) quite useful for computing the local epsilon factors and local $L$-functions, given one knows the local data.
Sep 15, 2019 at 15:02 history edited David Loeffler CC BY-SA 4.0
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Sep 15, 2019 at 14:56 history answered David Loeffler CC BY-SA 4.0