Abstract
This paper is an announcement of the following result, whose proof will be forthcoming. Let F be a totally real number field, and let \(F \subset K \subset L\) be a tower of fields with L / F a finite abelian extension. Let I denote the kernel of the natural projection from \(\mathbf {Z}[\mathrm{Gal}(L/F)]\) to \(\mathbf {Z}[\mathrm{Gal}(K/F)]\). Let \(\Theta \in \mathbf {Z}[\mathrm{Gal}(L/F)]\) denote the Stickelberger element encoding the special values at zero of the partial zeta functions of L / F, taken relative to sets S and T in the usual way. Let r denote the number of places in S that split completely in K. We show that \(\Theta \in I^{r}\), unless K is totally real in which case we obtain \(\Theta \in I^{r-1}\) and \(2\Theta \in I^r\). This proves a conjecture of Gross up to the factor of 2 in the case that K is totally real and \(\#S \ne r\). In this article we sketch the proof in the case that K is totally complex.
Résumé
Ce papier est une annonce du résultat suivant, dont la preuve est imminente. Soit F un corps de nombres totalement réel, et soit \(F \subset K \subset L\) une tour d’extensions, où l’extension L / F est abélienne finie. Soit I le noyau de la projection naturelle de \(\mathbf {Z}[\mathrm{Gal}(L/F)]\) vers \(\mathbf {Z}[\mathrm{Gal}(K/F)]\). Soit \(\Theta \in \mathbf {Z}[\mathrm{Gal}(L/F)]\) l’élément de Stickelberger qui encode les valeurs spéciales en zéro des fonctions zêta partielles de L / F, prise par rapport à des ensembles S et T de places de F de la manière usuelle. Soit r le nombre de places dans S qui sont totalement déployées dans K. Nous démontrons que \(\Theta \in I^r\), à moins que K ne soit totalement réel auquel cas nous obtenons \(\Theta \in I^{r-1}\) et \(2 \Theta \in I^r\). Ceci démontre une conjecture de Gross, à un facteur de 2 près dans le cas où K est totalement réel et \(\#S \ne r\). Dans cet article, nous esquissons une preuve dans le cas où l’extension K est totalement complexe.
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Notes
The conditions on T necessary for the Cassou-Noguès/Deligne–Ribet integrality statement below is that T contains two primes of different residue characteristic, or one place with residue characteristic p that is large enough. Here “large enough” depends on the value k at which \(\Theta \) will be evaluated; for \(k=0\), \(p \ge n+2\) is large enough. We will impose additional conditions on T for the use of Shintani’s method in the next section.
We are grateful to C. Popescu for suggesting that we strengthen our result in this form at the conference.
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Dedicated to Glenn Stevens on the occasion of his 60th birthday.
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Dasgupta, S., Spieß, M. The Eisenstein cocycle and Gross’s tower of fields conjecture. Ann. Math. Québec 40, 355–376 (2016). https://doi.org/10.1007/s40316-015-0046-2
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DOI: https://doi.org/10.1007/s40316-015-0046-2