Ax–Lindemann and André–Oort for a Nonholomorphic Modular Function
Journal de théorie des nombres de Bordeaux, Volume 30 (2018) no. 3, pp. 743-779.

The modular case of the André–Oort Conjecture is a theorem of André and Pila, having at its heart the well-known modular function j. I give an overview of two other “nonclassical” classes of modular function, namely the quasimodular (QM) and almost holomorphic modular (AHM) functions. These are perhaps less well-known than j, but have been studied by various authors including for example Masser, Shimura and Zagier. It turns out to be sufficient to focus on a particular QM function χ and its dual AHM function χ * , since these (together with j) generate the relevant fields. After discussing some of the properties of these functions, I go on to prove some Ax–Lindemann results about χ and χ * . I then combine these with a fairly standard method of o-minimality and point counting to prove the central result of the paper; a natural analogue of the modular André–Oort conjecture for the function χ * .

Le cas modulaire de la Conjecture d’André–Oort est un théorème démontré par André et Pila, qui concerne la fonction modulaire bien connue j. Je décris deux autres classes « non classiques » de la fonction modulaire, à savoir les fonctions quasimodulaires (QM) et presque holomorphes modulaires (AHM). Celles-ci sont peut-être moins connues que j, mais divers auteurs, y compris Masser, Shimura et Zagier, les ont étudiées. Il suffit de se concentrer sur une fonction QM précise χ et sa fonction AHM duale χ * , car celles-ci (avec j) engendrent les corps concernés. Après avoir discuté certaines des propriétés de ces fonctions, je montre par la suite quelques résultats de type Ax–Lindemann sur χ et χ * . Je les combine ensuite avec une méthode ordinaire de o-minimalité et de comptage de points pour démontrer le résultat central de l’article ; une analogique naturelle de la conjecture d’André–Oort modulaire qui s’applique à la fonction χ * .

Published online:
DOI: 10.5802/jtnb.1048
Classification: 11G18, 03C64
Keywords: Definable set, rational point, André–Oort conjecture, nonholomorphic modular function, Pila–Wilkie Theorem
Spence, Haden 1

1 2 Dennis Close, Aston Clinton, Buckinghamshire, HP22 5US, UK
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     title = {Ax{\textendash}Lindemann and {Andr\'e{\textendash}Oort} for a {Nonholomorphic} {Modular} {Function}},
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Spence, Haden. Ax–Lindemann and André–Oort for a Nonholomorphic Modular Function. Journal de théorie des nombres de Bordeaux, Volume 30 (2018) no. 3, pp. 743-779. doi : 10.5802/jtnb.1048.

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