Sphere bundles and spin (Ex)
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− | * For $k\geq2$, determine the number of distinct $S^k$-bundles over $S^2$. | + | * For $k\geq2$, determine the number of distinct linear $S^k$-bundles over $S^2$. |
* Let $E_k\to S^2$ be the complex plane bundle with Euler number $k$. Explain how to obtain the sphere-bundle $S(E_k)$ via surgery on $S^3$. | * Let $E_k\to S^2$ be the complex plane bundle with Euler number $k$. Explain how to obtain the sphere-bundle $S(E_k)$ via surgery on $S^3$. | ||
− | For $m\geq 4$ and $M$ a smooth closed manifold, let $S^1\hookrightarrow M^m$ be a nullhomotopic embedding. For $M$ spin, show that there is more than one possible effect for a surgery on this embedding. | + | For $m\geq 4$ and $M$ a smooth closed manifold, let $S^1\hookrightarrow M^m$ be a nullhomotopic embedding. For $M$ spin, show that ''a priori'' there is more than one possible effect for a surgery on this embedding. |
Now suppose $M$ is simply connected. For $M$ not spin, show that the effect of a surgery on this embedding ''is'' uniquely determined (difficult!). | Now suppose $M$ is simply connected. For $M$ not spin, show that the effect of a surgery on this embedding ''is'' uniquely determined (difficult!). |
Revision as of 22:57, 19 March 2012
- For , determine the number of distinct linear -bundles over .
- Let be the complex plane bundle with Euler number . Explain how to obtain the sphere-bundle via surgery on .
For and a smooth closed manifold, let be a nullhomotopic embedding. For spin, show that a priori there is more than one possible effect for a surgery on this embedding.
Now suppose is simply connected. For not spin, show that the effect of a surgery on this embedding is uniquely determined (difficult!).