Abstract
In this computational paper we verify a truncated version of the Buzzard–Calegari conjecture on the Newton polygon of the Hecke operator \(T_2\) for all large enough weights. We first develop a formula for computing p-adic valuations of exponential sums, which we then implement to compute 2-adic valuations of traces of Hecke operators acting on spaces of cusp forms. Finally, we verify that if Newton polygon of the Buzzard–Calegari polynomial has a vertex at \(n\le 15\), then it agrees with the Newton polygon of \(T_2\) up to n.
Résumé
Dans cet article, nous vérifions une version tronquée de la conjecture de Buzzard–Calegari concernant le polygone de Newton de l’opérateur Hecke \(T_2\) pour tous les poids suffisamment grands. Nous développons d’abord une formule pour les valuations p-adiques de sommes exponentielles, que nous utilisons ensuite pour calculer les valuations 2-adiques des traces d’opérateurs de Hecke agissant sur des espaces de formes cuspidales. Enfin, nous vérifions que si le polygone de Newton du polynôme de Buzzard–Calegari a un sommet en \(n\le 15\), alors il coïncide avec le polygone de Newton de \(T_2\) jusqu’à n.
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Acknowledgements
We are grateful to Damien Roy for many useful suggestions, and especially for showing us the proof of Proposition 7, to the anonymous referee for encouraging us to work out the relationship between the Newton polygons of \(P_{T_2}\) and its truncation, and to John Bergdall for helpful conversations.
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Appendix: 2-adic valuations of the traces of \(T_2\)
Appendix: 2-adic valuations of the traces of \(T_2\)
In the following table, for each \(n\le 5\) we make explicit the terms that appear in \(v_2({\text {Tr}}(\wedge ^n T_p|S_{2k}))\) from Theorem 12, and those defining the sequence \(a_n\) from Eq. (3) in Sect. 5. The 2-adic numbers \(\Omega _i\) are given modulo \(2^{50}\).
The complete table for all \(n\le 15\) is available online [7].
n | \(v_2(k-\Omega _i)\) or \(\min (n_j, 2 v_2(k-u_j))\) in \(v_2({\text {Tr}}(\wedge ^n T_2|S_{2k}))\) | \(v_2(k-\ell )\) in \(a_n\) | \(v_2(\Omega _i-\ell )\) or \(v_2(u_j-\ell )\) |
---|---|---|---|
1 | \(v_2(k- 442980431217671)\) | \(v_2(k-7)\) | 10 |
2 | \(v_2(k-791247700865546)\) | \(v_2(k-10)\) | 9 |
\(v_2(k-31828396041227)\) | \(v_2(k-11)\) | 10 | |
\(v_2(k-335062469580877)\) | \(v_2(k-13)\) | 6 | |
3 | \(v_2(k-48255093739981)\) | \(v_2(k-13)\) | 6 |
\(v_2(k-895017375933454)\) | \(v_2(k-14)\) | 10 | |
\(v_2(k-16843008520207)\) | \(v_2(k-15)\) | 12 | |
\(v_2(k-250702637217616)\) | \(v_2(k-16)\) | 6 | |
\(v_2(k-46624142875857)\) | \(v_2(k-17)\) | 6 | |
\(v_2(k-474794944364563)\) | \(v_2(k-19)\) | 28 | |
4 | \(v_2(k-798532487856848)\) | \(v_2(k-16)\) | 6 |
\(v_2(k-658899949170001)\) | \(v_2(k-17)\) | 6 | |
\(v_2(k-568752135614482)\) | \(v_2(k-18)\) | 12 | |
\(\min (15, 2 \cdot v_2(k - 19))\) | \(2\cdot v_2(k-19)\) | \(\infty \) | |
\(v_2(k-1103383114654676)\) | \(v_2(k-20)\) | 6 | |
\(v_2(k-60661288646421)\) | \(v_2(k-21)\) | 8 | |
\(v_2(k-1080512839942166)\) | \(v_2(k-22)\) | 31 | |
\(v_2(k-339362545926167)\) | \(v_2(k-23)\) | 33 | |
\(v_2(k-824086375843865)\) | \(v_2(k-25)\) | 11 | |
5 | \(v_2(k-912948839579667)\) | \(v_2(k-19)\) | 19 |
\(v_2(k-929666093061716)\) | \(v_2(k-20)\) | 6 | |
\(v_2(k-1090275108829461)\) | \(v_2(k-21)\) | 8 | |
\(\min (15, 2 \cdot v_2(k - 22))\) | \(2\cdot v_2(k-22)\) | \(\infty \) | |
\(\min (16, 2 \cdot v_2(k - 151))\) | \(2\cdot v_2(k-23)\) | 7 | |
\(v_2(k-215022683507480)\) | \(v_2(k-24)\) | 8 | |
\(v_2(k-188349340154137)\) | \(v_2(k-25)\) | 8 | |
\(v_2(k-25411498307609)\) | \(v_2(k-25)\) | 12 | |
\(v_2(k-255292856074266)\) | \(v_2(k-26)\) | 36 | |
\(v_2(k-893284478091291)\) | \(v_2(k-27)\) | 36 | |
\(v_2(k-378319707637788)\) | \(v_2(k-28)\) | 11 | |
\(v_2(k-436532622338077)\) | \(v_2(k-29)\) | 11 | |
\(v_2(k-669602715533343)\) | \(v_2(k-31)\) | 27 |
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Chiriac, L., Jorza, A. Newton polygons of Hecke operators. Ann. Math. Québec 45, 271–290 (2021). https://doi.org/10.1007/s40316-020-00149-z
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DOI: https://doi.org/10.1007/s40316-020-00149-z