SMS scnews item created by Stephan Tillmann at Tue 26 Apr 2016 1107
Type: Seminar
Distribution: World
Expiry: 26 Jul 2016
Calendar1: 4 May 2016 1200-1300
CalLoc1: Carslaw 535A
CalTitle1: Complements of connected hypersurfaces in \(S^4\)
Auth: tillmann@p710.pc (assumed)

Geometry & Topology

Complements of connected hypersurfaces in \(S^4\)

Jonathan Hillman (Sydney)

Wednesday 4 May 2016 from 12:00–13:00 in Carslaw 535A

Please join us for lunch after the talk!

Abstract: If \(M\) is a closed hypersurface in \(S^4=X\cup_MY\) and \(\beta=\beta_1(M)\) then elementary arguments using Mayer-Vietoris and duality show that \(\chi(X)+\chi(Y)=2\), \(1-\beta\leq\chi(X)\leq1+\beta\) and \(\chi(X)\equiv1-\beta\quad{mod}~(2)\). We shall give examples where these values are all realized, and where some or most are not realizable. If one of the complementary regions \(X\), say, is not simply-connected (e.g., if \(\beta>0\)) then there are infinitely many embeddings with a complementary region having Euler characteristic \(\chi(X)\) but distinct fundamental group. The constructions are in terms of framed link presentations for \(M\) (and 2-knot surgery for the result on \(\pi_1(X)\)); the obstructions are related to the lower central series of \(\pi_1(M)\) variously through an old theorem of Stallings or via the dual notion of Massey product.

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