Shadow-complexity and trisection genus
[Complexité ombre et genre de trisection]
Annales de la Faculté des sciences de Toulouse : Mathématiques, Série 6, Tome 34 (2025) no. 5, pp. 1185-1217

The shadow-complexity is an invariant of closed $4$-manifolds defined by using $2$-dimensional polyhedra called Turaev’s shadows, which, roughly speaking, measures how complicated a $2$-skeleton of the $4$-manifold is. In this paper, we define a new version $\mathrm{sc}_{r}$ of shadow-complexity depending on an extra parameter $r\ge 0$, and we investigate the relationship between this complexity and the trisection genus $g$. More explicitly, we prove an inequality $g(W) \le 2+2\mathrm{sc}_{r}(W)$ for any closed $4$-manifold $W$ and any $r\ge 1/2$. Moreover, we determine the exact values of $\mathrm{sc}_{1/2}$ for infinitely many $4$-manifolds, and also we classify all the closed $4$-manifolds with $\mathrm{sc}_{1/2}\le 1/2$.

La complexité ombre est un invariant de variétés de dimension $4$ défini en utilisant des polyèdres de dimension $2$, appelés les « ombres de Turaev », qui, de façon simplifiée, mesure la complexité d’un $2$-squelette de la $4$-variété. Dans cet article, nous définissons une version de la complexité ombre $\mathrm{sc}_{r}$ dépendant d’un paramètre supplémentaire $r\ge 0$, et nous investiguons les liens entre cette complexité et le genre de trisection $g$. Plus explicitement, nous prouvons l’inégalité $g(W) \le 2+2\mathrm{sc}_{r}(W)$ pour toute $4$-variété fermée et tout $r\ge 1/2$. De plus, nous déterminons les valeurs exactes de $\mathrm{sc}_{1/2}$ pour une famille infinie de $4$-variétés, et nous classifions toutes les $4$-variétés fermées avec $\mathrm{sc}_{1/2}\le 1/2$.

Reçu le :
Accepté le :
Publié le :
DOI : 10.5802/afst.1830
Classification : 57K41, 57Q15, 57R65
Keywords: $4$-manifolds, shadows, shadow-complexity, trisections, trisection genus

Hironobu Naoe 1 ; Masaki Ogawa 2

1 Institute of Science Tokyo, Department of Mathematics, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551 (Japan)
2 Tohoku University Mathematical Science Center for Co-creative Society, Aoba-6-3 Aramaki, Aoba-ku, Sendai, Miyagi, 980-0845 (Japan)
Licence : CC-BY 4.0
Droits d'auteur : Les auteurs conservent leurs droits
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Hironobu Naoe; Masaki Ogawa. Shadow-complexity and trisection genus. Annales de la Faculté des sciences de Toulouse : Mathématiques, Série 6, Tome 34 (2025) no. 5, pp. 1185-1217. doi: 10.5802/afst.1830

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