[Surfaces moyennes dans l’espace half-pipe et théorie de Teichmüller infinitésimale]
We study a correspondence between smooth spacelike surfaces in the half-pipe space $\mathbb{HP}^3$ and divergence-free vector fields on the hyperbolic plane $\mathbb{H}^2$. We show that a particular case involves harmonic Lagrangian vector fields on $\mathbb{H}^2$, which are related to mean surfaces in $\mathbb{HP}^3$. Consequently, we prove that the infinitesimal Douady-Earle extension is a harmonic Lagrangian vector field that corresponds to a mean surface in $\mathbb{HP}^3$ with prescribed boundary data at infinity.
We establish both existence and, under certain assumptions, uniqueness results for harmonic Lagrangian extension of a vector field on the circle. Finally, we characterize the Zygmund and little Zygmund conditions and provide quantitative bounds in terms of the half-pipe width.
Nous étudions une correspondance entre les surfaces lisses de type espace dans l’espace half-pipe $\mathbb{HP}^3$ et les champs de vecteurs à divergence nulle sur le plan hyperbolique $\mathbb{H}^2$. Nous montrons qu’un cas particulier de cette correspondance fait intervenir des champs de vecteurs harmoniques lagrangiens sur $\mathbb{H}^2$, qui sont liés aux surfaces moyennes dans $\mathbb{HP}^3$. Par conséquent, nous prouvons que l’extension infinitésimale de Douady–Earle est un champ de vecteurs harmonique lagrangien correspondant à une surface moyenne dans $\mathbb{HP}^3$, avec un bord prescrit à l’infini.
Nous établissons à la fois des résultats d’existence et, sous certaines hypothèses, d’unicité d’extension harmonique lagrangienne d’un champ de vecteurs défini sur le cercle. Enfin, nous caractérisons les conditions de Zygmund et de petit Zygmund, et nous fournissons des estimations quantitatives en termes de largeur de l’espace half-pipe.
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Keywords: Half-pipe space, Minkowski space, hyperbolic plane, mean surfaces, harmonic vector fields
Mots-clés : Espace half-pipe, espace de Minkowski, plan hyperbolique, surfaces moyennes, champs de vecteurs harmoniques
Farid Diaf 1

@article{JEP_2025__12__1289_0, author = {Farid Diaf}, title = {Mean surfaces in half-pipe space and infinitesimal {Teichm\"uller} theory}, journal = {Journal de l{\textquoteright}\'Ecole polytechnique {\textemdash} Math\'ematiques}, pages = {1289--1343}, publisher = {\'Ecole polytechnique}, volume = {12}, year = {2025}, doi = {10.5802/jep.311}, language = {en}, url = {https://jep.centre-mersenne.org/articles/10.5802/jep.311/} }
TY - JOUR AU - Farid Diaf TI - Mean surfaces in half-pipe space and infinitesimal Teichmüller theory JO - Journal de l’École polytechnique — Mathématiques PY - 2025 SP - 1289 EP - 1343 VL - 12 PB - École polytechnique UR - https://jep.centre-mersenne.org/articles/10.5802/jep.311/ DO - 10.5802/jep.311 LA - en ID - JEP_2025__12__1289_0 ER -
%0 Journal Article %A Farid Diaf %T Mean surfaces in half-pipe space and infinitesimal Teichmüller theory %J Journal de l’École polytechnique — Mathématiques %D 2025 %P 1289-1343 %V 12 %I École polytechnique %U https://jep.centre-mersenne.org/articles/10.5802/jep.311/ %R 10.5802/jep.311 %G en %F JEP_2025__12__1289_0
Farid Diaf. Mean surfaces in half-pipe space and infinitesimal Teichmüller theory. Journal de l’École polytechnique — Mathématiques, Tome 12 (2025), pp. 1289-1343. doi : 10.5802/jep.311. https://jep.centre-mersenne.org/articles/10.5802/jep.311/
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