Theta operator equals Fontaine operator on modular curves
[L’opérateur thêta et l’opérateur de Fontaine sur les courbes modulaires]
Journal de l’École polytechnique — Mathématiques, Tome 13 (2026), pp. 349-398

Inspired by [Pan26], we give a new proof that for an overconvergent modular eigenform $f$ of weight $1+k$ with $k\in \mathbb{Z}_{\ge 1}$, assuming that its associated Galois representation $\rho _{f}:\mathrm{Gal}_{\mathbb{Q}}\rightarrow \mathrm{GL}_{2}(\overline{\mathbb{Q}}_{p})$ is irreducible, then $f$ is classical if and only if the associated Galois representation $\rho _{f}$ is de Rham at $p$. For the proof, we prove that theta operator $\theta ^{k}$ coincides with Fontaine operator in a suitable sense.

En nous inspirant de [Pan26], nous donnons une nouvelle preuve du fait que pour une forme modulaire surconvergente $f$ de poids $1+k$ avec $k\in \mathbb{Z}_{\ge 1}$, si sa représentation galoisienne associée $\rho _{f}:\mathrm{Gal}_{\mathbb{Q}}\rightarrow \mathrm{GL}_{2}(\overline{\mathbb{Q}}_{p})$ est irréductible, alors $f$ est classique si et seulement si $\rho _{f}$ est de Rham en $p$. Pour ce faire, nous démontrons que l’opérateur thêta $\theta ^{k}$ coïncide avec l’opérateur de Fontaine en un sens convenable.

Reçu le :
Accepté le :
Publié le :
DOI : 10.5802/jep.329
Classification : 14G35, 11F17, 11F18
Keywords: Perfectoid modular curve, Fontaine operator, classicality
Mots-clés : Courbe modulaire perfectoïde, opérateur de Fontaine, classicité

Yuanyang Jiang  1

1 Institut Mathématiques d’Orsay, Université Paris-Saclay, Bât. 307, 91400 Orsay, France
Licence : CC-BY 4.0
Droits d'auteur : Les auteurs conservent leurs droits
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     title = {Theta operator equals {Fontaine} operator on modular curves},
     journal = {Journal de l{\textquoteright}\'Ecole polytechnique {\textemdash} Math\'ematiques},
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Yuanyang Jiang. Theta operator equals Fontaine operator on modular curves. Journal de l’École polytechnique — Mathématiques, Tome 13 (2026), pp. 349-398. doi: 10.5802/jep.329

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