Configuration spaces on a wedge of spheres and Hochschild–Pirashvili homology
[Espaces de configuration sur un bouquet de sphères et homologie de Hochschild–Pirashvili]
Annales Henri Lebesgue, Tome 7 (2024), pp. 841-902

We study the compactly supported rational cohomology of configuration spaces of points on wedges of spheres, equipped with natural actions of the symmetric group and the group Out(F g ) of outer automorphisms of the free group. These representations show up in seemingly unrelated parts of mathematics, from cohomology of moduli spaces of curves to polynomial functors on free groups and Hochschild–Pirashvili cohomology.

We show that these cohomology representations form a polynomial functor, and use various geometric models to compute many of its composition factors. We further compute the composition factors completely for all configurations of n10 points. An application of this analysis is a new super-exponential lower bound on the symmetric group action on the weight 0 component of H c * ( 2,n ).

Nous étudions la cohomologie rationnelle à support compact des espaces de configurations de points sur les bouquets de sphères, équipée d’actions naturelles du groupe symétrique et du groupe Out(F g ) des automorphismes extérieurs du groupe libre. Ces représentations apparaissent dans des parties qui ne semblent pas avoir de lien entre elles, notamment la cohomologie des espaces de modules de courbes ainsi que les foncteurs polynomiaux sur les groupes libres et la cohomologie de Hochschild–Pirashvili.

Nous prouvons que ces représentations obtenues par la cohomologie ont une structure de foncteur polynomial et utilisons divers modèles géométriques pour calculer une grande quantité de leurs facteurs de composition. De plus, nous calculons complètement les facteurs de composition pour toutes les configurations de n10 points. Comme application de cette analyse, nous obtenons une nouvelle borne inférieure à croissance super-exponentielle pour l’action du groupe symétrique sur la composante de poids 0 de H c * ( 2,n ).

Reçu le :
Accepté le :
Publié le :
DOI : 10.5802/ahl.213
Classification : 55R80, 14H10, 14Q05, 13D03
Keywords: configuration spaces, polynomial functors, moduli spaces

Gadish, Nir  1   ; Hainaut, Louis  2

1 Department of Mathematics, University of Michigan, 530 Church St, Ann Arbor, MI 48109 (USA)
2 Stockholm University, Department of Mathematics, 106 91 Stockholm (Sweden)
Licence : CC-BY 4.0
Droits d'auteur : Les auteurs conservent leurs droits
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Gadish, Nir; Hainaut, Louis. Configuration spaces on a wedge of spheres and Hochschild–Pirashvili homology. Annales Henri Lebesgue, Tome 7 (2024), pp. 841-902. doi: 10.5802/ahl.213

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