Let X → B be an orientable sphere bundle. Its Gysin sequence exhibits H∗(X) as an extension of H∗(B)–modules. We prove that the class of this extension is the image of a canonical class that we define in the Hochschild 3–cohomology of H∗(B), corresponding to a component of its A∞–structure, and generalizing the Massey triple product. We identify two cases where this class vanishes, so that the Gysin extension is split. The first, with rational coefficients, is that where B is a formal space; the second, with integer coefficients, is where B is a torus.
Berrick, A J  1 ; Davydov, A A  2
@article{10_2140_agt_2001_1_743,
author = {Berrick, A J and Davydov, A A},
title = {Splitting of {Gysin} extensions},
journal = {Algebraic and Geometric Topology},
pages = {743--762},
year = {2001},
volume = {1},
number = {2},
doi = {10.2140/agt.2001.1.743},
url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2001.1.743/}
}
Berrick, A J; Davydov, A A. Splitting of Gysin extensions. Algebraic and Geometric Topology, Tome 1 (2001) no. 2, pp. 743-762. doi: 10.2140/agt.2001.1.743
[1] , , Homological algebra, Princeton University Press (1956)
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