Manifolds with singularities
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Malte Röer (Talk | contribs) |
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===<wikitex>$\Sigma$-manifolds</wikitex>=== | ===<wikitex>$\Sigma$-manifolds</wikitex>=== | ||
<wikitex> | <wikitex> | ||
− | Following ({{cite|Botvinnik2001}}, {{cite|Botvinnik1992}}), a definition can be given | + | Following ({{cite|Botvinnik2001}}, {{cite|Botvinnik1992}}), a more general definition can be given. Let $(P_1 , ..., P_k)$ be a (possibly empty) collection of closed manifolds and denote by $P_0$ the set containing only one point. Then define $\Sigma_k := (P_0, P_1, ... , P_k)$. For a subset $I = \{i_1,..., i_q\} \subset \{0,...,k\}$ define $P^I := P_{i_1} \times ...\times P_{i_q}$. |
− | {{beginthm| | + | {{beginthm|Definition}}A manifold $M$ is a $\Sigma_k$-Manifold if |
# there is a partition $\partial M = \partial_0 M \cup ... \cup \partial_k M$, such that $\partial_I M := \partial_{i_1} \cap ... \cap \partial_{i_q} M$ is a manifold for each $I = \{i_1,...,i_q\} \subset \{0,...,k\}$, and such that | # there is a partition $\partial M = \partial_0 M \cup ... \cup \partial_k M$, such that $\partial_I M := \partial_{i_1} \cap ... \cap \partial_{i_q} M$ is a manifold for each $I = \{i_1,...,i_q\} \subset \{0,...,k\}$, and such that | ||
$$ \partial (\partial_I M) = \cup_{j \notin I} \partial_j M \cap \partial_I M $$. | $$ \partial (\partial_I M) = \cup_{j \notin I} \partial_j M \cap \partial_I M $$. | ||
− | # | + | # for each $I \subset \{0,...,k\}$ there is a manifold $\beta_I M$ and a diffeomorphism |
+ | $$ \phi_I: \partial_I M \rightarrow \beta_I M \times P^I$$ , | ||
+ | such that if $J \subset I$ and $\iota: \partial_I M \rightarrow \partial_J M$ is the inclusion, then the composition | ||
+ | $$ \phi_J \circ \iota \circ \phi_I^{-1}: \beta_I M \times P^I \rightarrow \beta_J M \times P^J$$ | ||
+ | restricts to the identity on the factor $P^J$ in $P^I$. The diffeomorphisms $\phi_I$ are called product structures. | ||
+ | {{endthm|Definition}} | ||
+ | On a $\Sigma_k$-manifold $M$, there is a canonical equivalence relation $\sim$: two points $x,y \in M$ are defined to be equivalent if there is an $I \subset \{0,...,k\}$ such that $x,y \in \partial_I M$ and $pr \circ \phi_I(x) = pr \circ \phi_I(y)$, where $pr: \beta_I M \times P^I \rightarrow \beta_I M$ is the projection. | ||
+ | Now we can give a general definition: a manifold with a $\Sigma_k$-singularity is a topological space $\overline{A}$ of the form | ||
+ | $$ \overline{A} = A / \sim $$ | ||
+ | for a $\Sigma_k$-manifold $A$. | ||
+ | The spaces defined above as manifolds with a $P_1$-singularity are contained in this more general definition. In fact, they give the manifolds with a $\Sigma_1$-singularity. For given a manifold $P_1$, set $\Sigma_1 = (P_0, P_1)$. Then the manifold $A$ with boundary $A(1) \times P_1$, which appears in the above definition, is a $\Sigma_1$-manifold. The attachement of the cone-end $A(1) \times C P_1$ now corresponds to the collapsing of the equivalence relation $\sim$ in $A$. | ||
</wikitex> | </wikitex> | ||
− | == | + | == Some examples == |
+ | ===Intersecting spheres=== | ||
<wikitex>; | <wikitex>; | ||
− | ... | + | A basic example is presented by two spheres intersecting each other in a sphere of lower dimension. Choose an embedding $i: S^{n-1} \rightarrow S^n$. Then define $\overline{S} := S^n \cup_{j(S^{n-1}} S^n$. Outside of the intersecting sphere $j(S^{n-1})$ this is an $n$-dimensional manifold. The intersecting sphere itself has a neigborhood homeomorphic to the product of $S^{n-1}$ and a cone over $\Zz_4$ . We can write $\overline{S} = D^n \times \Zz_4 \cup_{S^{n-1} \times \Zz_4} S^{n-1} \times C \Zz_4$. |
+ | </wikitex> | ||
+ | ===Inverse images of critical points=== | ||
+ | <wikitex>; | ||
+ | Let $f:\Rr^n \rightarrow \Rr$ be a Morse-function with $0$ as a single critical point. We can suppose that $f(x) = -x^2_1 -...-x^2_k + x^2_{k+1} + ... + x^2_n$ near $0$. Setting $M := f^{-1}(\{0\})$, we see that the cone $C S^{k-1} \times S^{n-k-1} = \{t \cdot x : 0 \leq t \leq 1 , x \in S^{k-1} \times S^{n-k-1} \subset \Rr^n \}$ provides a neighborhood of $0$ in $M$. It follows that $M$ is of the form $ | ||
</wikitex> | </wikitex> | ||
Revision as of 17:03, 7 June 2010
Contents |
1 Introduction
Manifolds with singularities are geometric objects in topology generalizing manifolds. They were introduced in ([Sullivan1996],[Sullivan1967]) and [Baas1973]. Applications of the concept include representing cycles in homology theories with coefficients.
2 Definitions
2.1 Cone-like singularities
A manifold with singularities of Baas-Sullivan type is a topological space that looks like a manifold outside of a compact 'singularity set', while the singularity set has a neighborhood that looks like the product of manifold and a cone. Here is a precise definition. Let be a closed manifold. A manifold with a -singularity (following [Baas1973]) is a space of the form
Here, is a manifold with boundary .
2.2 -manifolds
Following ([Botvinnik2001], [Botvinnik1992]), a more general definition can be given. Let be a (possibly empty) collection of closed manifolds and denote by the set containing only one point. Then define . For a subset define .
Tex syntax erroris a -Manifold if
- there is a partition , such that is a manifold for each , and such that
- for each there is a manifold and a diffeomorphism
such that if and is the inclusion, then the composition
restricts to the identity on the factor in . The diffeomorphisms are called product structures.
Tex syntax error, there is a canonical equivalence relation : two points are defined to be equivalent if there is an such that and , where is the projection.
Now we can give a general definition: a manifold with a -singularity is a topological space of the form
for a -manifold .
The spaces defined above as manifolds with a -singularity are contained in this more general definition. In fact, they give the manifolds with a -singularity. For given a manifold , set . Then the manifold with boundary , which appears in the above definition, is a -manifold. The attachement of the cone-end now corresponds to the collapsing of the equivalence relation in .
3 Some examples
3.1 Intersecting spheres
A basic example is presented by two spheres intersecting each other in a sphere of lower dimension. Choose an embedding . Then define . Outside of the intersecting sphere this is an -dimensional manifold. The intersecting sphere itself has a neigborhood homeomorphic to the product of and a cone over . We can write .
3.2 Inverse images of critical points
Tex syntax error. It follows that
Tex syntax erroris of the form $
4 Invariants
...
5 Classification/Characterization
...
6 Further discussion
...
7 References
- [Baas1973] N. A. Baas, On bordism theory of manifolds with singularities, Math. Scand. 33 (1973), 279–302 (1974). MR0346824 (49 #11547b) Zbl 0281.57027
- [Botvinnik1992] B. I. Botvinnik, Manifolds with singularities and the Adams-Novikov spectral sequence, Cambridge University Press, Cambridge, 1992. MR1192127 (93h:55002) Zbl 0764.55001
- [Botvinnik2001] B. Botvinnik, Manifolds with singularities accepting a metric of positive scalar curvature, Geom. Topol. 5 (2001), 683–718 (electronic). MR1857524 (2002j:57045) Zbl 1002.57055
- [Sullivan1967] D. Sullivan, On the Hauptvermutung for manifolds, Bull. Amer. Math. Soc. 73 (1967), 598–600. MR0212811 (35 #3676) Zbl 0153.54002
- [Sullivan1996] D. P. Sullivan, Triangulating and smoothing homotopy equivalences and homeomorphisms. Geometric Topology Seminar Notes, 1 (1996), 69–103. MR1434103 (98c:57027) Zbl 0871.57021
This page has not been refereed. The information given here might be incomplete or provisional. |
Here, is a manifold with boundary .
2.2 -manifolds
Following ([Botvinnik2001], [Botvinnik1992]), a more general definition can be given. Let be a (possibly empty) collection of closed manifolds and denote by the set containing only one point. Then define . For a subset define .
Tex syntax erroris a -Manifold if
- there is a partition , such that is a manifold for each , and such that
- for each there is a manifold and a diffeomorphism
such that if and is the inclusion, then the composition
restricts to the identity on the factor in . The diffeomorphisms are called product structures.
Tex syntax error, there is a canonical equivalence relation : two points are defined to be equivalent if there is an such that and , where is the projection.
Now we can give a general definition: a manifold with a -singularity is a topological space of the form
for a -manifold .
The spaces defined above as manifolds with a -singularity are contained in this more general definition. In fact, they give the manifolds with a -singularity. For given a manifold , set . Then the manifold with boundary , which appears in the above definition, is a -manifold. The attachement of the cone-end now corresponds to the collapsing of the equivalence relation in .
3 Some examples
3.1 Intersecting spheres
A basic example is presented by two spheres intersecting each other in a sphere of lower dimension. Choose an embedding . Then define . Outside of the intersecting sphere this is an -dimensional manifold. The intersecting sphere itself has a neigborhood homeomorphic to the product of and a cone over . We can write .
3.2 Inverse images of critical points
Tex syntax error. It follows that
Tex syntax erroris of the form $
4 Invariants
...
5 Classification/Characterization
...
6 Further discussion
...
7 References
- [Baas1973] N. A. Baas, On bordism theory of manifolds with singularities, Math. Scand. 33 (1973), 279–302 (1974). MR0346824 (49 #11547b) Zbl 0281.57027
- [Botvinnik1992] B. I. Botvinnik, Manifolds with singularities and the Adams-Novikov spectral sequence, Cambridge University Press, Cambridge, 1992. MR1192127 (93h:55002) Zbl 0764.55001
- [Botvinnik2001] B. Botvinnik, Manifolds with singularities accepting a metric of positive scalar curvature, Geom. Topol. 5 (2001), 683–718 (electronic). MR1857524 (2002j:57045) Zbl 1002.57055
- [Sullivan1967] D. Sullivan, On the Hauptvermutung for manifolds, Bull. Amer. Math. Soc. 73 (1967), 598–600. MR0212811 (35 #3676) Zbl 0153.54002
- [Sullivan1996] D. P. Sullivan, Triangulating and smoothing homotopy equivalences and homeomorphisms. Geometric Topology Seminar Notes, 1 (1996), 69–103. MR1434103 (98c:57027) Zbl 0871.57021
This page has not been refereed. The information given here might be incomplete or provisional. |
Here, is a manifold with boundary .
2.2 -manifolds
Following ([Botvinnik2001], [Botvinnik1992]), a more general definition can be given. Let be a (possibly empty) collection of closed manifolds and denote by the set containing only one point. Then define . For a subset define .
Tex syntax erroris a -Manifold if
- there is a partition , such that is a manifold for each , and such that
- for each there is a manifold and a diffeomorphism
such that if and is the inclusion, then the composition
restricts to the identity on the factor in . The diffeomorphisms are called product structures.
Tex syntax error, there is a canonical equivalence relation : two points are defined to be equivalent if there is an such that and , where is the projection.
Now we can give a general definition: a manifold with a -singularity is a topological space of the form
for a -manifold .
The spaces defined above as manifolds with a -singularity are contained in this more general definition. In fact, they give the manifolds with a -singularity. For given a manifold , set . Then the manifold with boundary , which appears in the above definition, is a -manifold. The attachement of the cone-end now corresponds to the collapsing of the equivalence relation in .
3 Some examples
3.1 Intersecting spheres
A basic example is presented by two spheres intersecting each other in a sphere of lower dimension. Choose an embedding . Then define . Outside of the intersecting sphere this is an -dimensional manifold. The intersecting sphere itself has a neigborhood homeomorphic to the product of and a cone over . We can write .
3.2 Inverse images of critical points
Tex syntax error. It follows that
Tex syntax erroris of the form $
4 Invariants
...
5 Classification/Characterization
...
6 Further discussion
...
7 References
- [Baas1973] N. A. Baas, On bordism theory of manifolds with singularities, Math. Scand. 33 (1973), 279–302 (1974). MR0346824 (49 #11547b) Zbl 0281.57027
- [Botvinnik1992] B. I. Botvinnik, Manifolds with singularities and the Adams-Novikov spectral sequence, Cambridge University Press, Cambridge, 1992. MR1192127 (93h:55002) Zbl 0764.55001
- [Botvinnik2001] B. Botvinnik, Manifolds with singularities accepting a metric of positive scalar curvature, Geom. Topol. 5 (2001), 683–718 (electronic). MR1857524 (2002j:57045) Zbl 1002.57055
- [Sullivan1967] D. Sullivan, On the Hauptvermutung for manifolds, Bull. Amer. Math. Soc. 73 (1967), 598–600. MR0212811 (35 #3676) Zbl 0153.54002
- [Sullivan1996] D. P. Sullivan, Triangulating and smoothing homotopy equivalences and homeomorphisms. Geometric Topology Seminar Notes, 1 (1996), 69–103. MR1434103 (98c:57027) Zbl 0871.57021
This page has not been refereed. The information given here might be incomplete or provisional. |
Here, is a manifold with boundary .
2.2 -manifolds
Following ([Botvinnik2001], [Botvinnik1992]), a more general definition can be given. Let be a (possibly empty) collection of closed manifolds and denote by the set containing only one point. Then define . For a subset define .
Tex syntax erroris a -Manifold if
- there is a partition , such that is a manifold for each , and such that
- for each there is a manifold and a diffeomorphism
such that if and is the inclusion, then the composition
restricts to the identity on the factor in . The diffeomorphisms are called product structures.
Tex syntax error, there is a canonical equivalence relation : two points are defined to be equivalent if there is an such that and , where is the projection.
Now we can give a general definition: a manifold with a -singularity is a topological space of the form
for a -manifold .
The spaces defined above as manifolds with a -singularity are contained in this more general definition. In fact, they give the manifolds with a -singularity. For given a manifold , set . Then the manifold with boundary , which appears in the above definition, is a -manifold. The attachement of the cone-end now corresponds to the collapsing of the equivalence relation in .
3 Some examples
3.1 Intersecting spheres
A basic example is presented by two spheres intersecting each other in a sphere of lower dimension. Choose an embedding . Then define . Outside of the intersecting sphere this is an -dimensional manifold. The intersecting sphere itself has a neigborhood homeomorphic to the product of and a cone over . We can write .
3.2 Inverse images of critical points
Tex syntax error. It follows that
Tex syntax erroris of the form $
4 Invariants
...
5 Classification/Characterization
...
6 Further discussion
...
7 References
- [Baas1973] N. A. Baas, On bordism theory of manifolds with singularities, Math. Scand. 33 (1973), 279–302 (1974). MR0346824 (49 #11547b) Zbl 0281.57027
- [Botvinnik1992] B. I. Botvinnik, Manifolds with singularities and the Adams-Novikov spectral sequence, Cambridge University Press, Cambridge, 1992. MR1192127 (93h:55002) Zbl 0764.55001
- [Botvinnik2001] B. Botvinnik, Manifolds with singularities accepting a metric of positive scalar curvature, Geom. Topol. 5 (2001), 683–718 (electronic). MR1857524 (2002j:57045) Zbl 1002.57055
- [Sullivan1967] D. Sullivan, On the Hauptvermutung for manifolds, Bull. Amer. Math. Soc. 73 (1967), 598–600. MR0212811 (35 #3676) Zbl 0153.54002
- [Sullivan1996] D. P. Sullivan, Triangulating and smoothing homotopy equivalences and homeomorphisms. Geometric Topology Seminar Notes, 1 (1996), 69–103. MR1434103 (98c:57027) Zbl 0871.57021
This page has not been refereed. The information given here might be incomplete or provisional. |