Plumbing
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Let $G$ be a graph with vertices $\{v_1, \dots, v_n\}$ such that the edge set between $v_i$ and $v_j$, is non-empty only if $p_i = q_j$. We choose disjoint disks $D_{ij}$ in $M_i$ (one for each edge incident to $v_i$) | Let $G$ be a graph with vertices $\{v_1, \dots, v_n\}$ such that the edge set between $v_i$ and $v_j$, is non-empty only if $p_i = q_j$. We choose disjoint disks $D_{ij}$ in $M_i$ (one for each edge incident to $v_i$) | ||
and trivializations $D(\alpha_i)|_{D_{ij}}\cong D^{p_i} \times D^{q_i}$. | and trivializations $D(\alpha_i)|_{D_{ij}}\cong D^{p_i} \times D^{q_i}$. | ||
− | Finally we form the manifold $W = W(G;\{\alpha_i\})$ from the disjoint union of the $D(\alpha_i)$ by identifying, for each edge of $G$, the corresponding $D^{p_i | + | Finally we form the manifold $W = W(G;\{\alpha_i\})$ from the disjoint union of the $D(\alpha_i)$ by identifying, for each edge of $G$, the corresponding $D^{p_i} \times D^{q_i} \subseteq D(\alpha_i)$ and |
− | $D^{q_j | + | $D^{q_j} \times D^{p_j}\subseteq D(\alpha_j)$ with the standard diffeomorphism $(x,y)\mapsto (y,x)$, which interchanges |
base and fiber of the two bundles. | base and fiber of the two bundles. | ||
Revision as of 12:22, 31 March 2011
This page has not been refereed. The information given here might be incomplete or provisional. |
Contents |
1 Introduction
Plumbing is a gluing construction which takes as input some disk bundles over manifolds (frequently just spheres) with -dimensional total space and produces another -manifold with boundary. It identifies fibers of one bundle with disks in the base manifold of the other bundle and vice versa.
2 Construction
As special case of the following construction goes back at least to [Milnor1959].
Let , let be pairs of positive integers such that and let be a -dimensional vector bundle over the -dimensional manifold . We consider the corresponding disk bundles
Let be a graph with vertices such that the edge set between and , is non-empty only if . We choose disjoint disks in (one for each edge incident to ) and trivializations . Finally we form the manifold from the disjoint union of the by identifying, for each edge of , the corresponding and with the standard diffeomorphism , which interchanges base and fiber of the two bundles.
The manifold is the result of the plumbing, often one is mainly interested in its boundary .
3 Invariants
...
4 An important special case
If is simply connected and all the base manifolds are spheres then
is often a homotopy sphere. We establish some notation for graphs, bundles and define
- let denote the graph with two vertices and one edge connecting them and define ,
- let denote the -graph,
- let denote the tangent bundle of the -sphere,
- let , , denote a generator,
- let , denote a generator:
- let be the suspension homomorphism,
- for and for ,
- let be essential.
The plumbing construction can be used to produce exotic spheres:
- , the Milnor sphere, generates , .
- , the Kervaire sphere, generates .
- is the inverse of the Milnor sphere for .
- For general , is exotic.
- , generates .
- , generates .
5 References
- [Milnor1959] J. Milnor, Differentiable structures on spheres, Amer. J. Math. 81 (1959), 962–972. MR0110107 (22 #990) Zbl 0111.35501