The group of disjoint 2-spheres in 4-space

• 成果类型: Article
• 署名作者: Schneiderman, Rob; Teichner, Peter
• 刊物名称: ANNALS OF MATHEMATICS
• ISSN/ISSBN: 0003-486X
• DOI: 10.4007/annals.2019.190.3.1
• 发表日期: 2019
• 页码: 669-750
• 关键词: link homotopy; MAPS

摘要

We compute the group LM2,24 of link homotopy classes of link maps of two 2-spheres into 4-space. It turns out to be free abelian, generated by geometric constructions applied to the Fenn-Rolfsen link map and detected by two self-intersection invariants introduced by Kirk in this setting. As a corollary, we show that any link map with one topologically embedded component is link homotopic to the unlink. Our proof introduces a new basic link homotopy, which we call a Whitney homotopy, that shrinks an embedded Whitney sphere constructed from four copies of a Whitney disk. Freedman's disk embedding theorem is applied to get the necessary embedded Whitney disks, after constructing sufficiently many accessory spheres as algebraic duals for immersed Whitney disks. To construct these accessory spheres and immersed Whitney disks we use the algebra of metabolic forms over the group ring Z[Z], and we introduce a number of new 4-dimensional constructions, including maneuvers involving the boundary arcs of Whitney disks.