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Line bundles with c 1 L 2 = 0

Stefano De Michelis (1991)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We prove that on a C W -complex the obstruction for a line bundle L to be the fractional power of a suitable pullback of the Hopf bundle on a 2-dimensional sphere is the vanishing of the square of the first Chern class of L . On the other hand we show that if one looks at integral powers then further secondary obstructions exist.

Line bundles with c 1 L 2 = 0 . A six dimensional example

Stefano De Michelis (1991)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We exhibit a six dimensional manifold with a line bundle on it which is not the pullback of a bundle on S 2 .

Line bundles with c 1 L 2 = 0 . Higher order obstruction

Stefano De Michelis (1991)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We study secondary obstructions to representing a line bundle as the pull-back of a line bundle on S 2 and we interpret them geometrically.

Linking and coincidence invariants

Ulrich Koschorke (2004)

Fundamenta Mathematicae

Given a link map f into a manifold of the form Q = N × ℝ, when can it be deformed to an “unlinked” position (in some sense, e.g. where its components map to disjoint ℝ-levels)? Using the language of normal bordism theory as well as the path space approach of Hatcher and Quinn we define obstructions ω ̃ ε ( f ) , ε = + or ε = -, which often answer this question completely and which, in addition, turn out to distinguish a great number of different link homotopy classes. In certain cases they even allow a complete...

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