5-manifolds: 1-connected
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Contents |
1 Introduction
Tex syntax errorbe the set of diffeomorphism classes of closed, oriented, smooth, simply-connected 5-manifolds
Tex syntax errorand let
Tex syntax errorbe the subset of diffeomorphism classes of spinable manifolds. The calculation of
Tex syntax errorwas first obtained by Smale [Smale1962] and was one of the first applications of the h-cobordism theorem. A little latter Barden [Barden1965] devised an elegant surgery argument and applied results of [Wall1964] on the diffeomorphism groups of 4-manifolds to give an explicit and complete classification of all of
Tex syntax error.
Simply-connected 5-manifolds are an appealing class of manifolds: the dimension is just large enough so that the full power of surgery techniques can be applied but it is low enough that the manifolds are simple enough to be readily classified. A feature of simply-connected 5-manifolds is that the homotopy, homeomorphism and diffeomorphism classification all coincide. Note that not every simply-connected 5-dimensional Poincaré space is smoothable. The classification of simply-connected 5-dimensional Poincaré spaces was achieved by Stöcker [Stöcker1982].
2 Constructions and examples
We first list some familiar 5-manifolds using Barden's notation:
- .
- .
- , the total space of the non-trivial -bundle over .
- , the Wu-manifold, is the homogeneous space obtained from the standard inclusion of .
In [Barden1965, Section 1] a construction of simply-connected 5-manifolds is given by expressing them as twisted doubles where is a certain simply connected -manifold with boundary a simply-connected -manifold and is a diffeomorphism. Barden used results of [Wall1964] to show that diffeomorphisms realising the required ismorphisms of exist.
2.1 The general spin case
Next we present a construction of simply-connected spin 5-manifolds. A priori the construction depends upon choices, but applying Theorem 4.3 below shows that the choices do not affect the diffeomorphism type of the manifold constructed. Note that all homology groups are with integer coefficients.
Given a finitely generated abelian group , let denote the degree 2 Moore space with . The space may be realised as a finite CW-complex with only -cells and -cells and so there is an embedding . LetTex syntax errorbe a regular neighbourhood of and let
Tex syntax errorbe the boundary of
Tex syntax error. Then
Tex syntax erroris a closed, smooth, simply-connected, spinable 5-manifold with where is the torsion subgroup of . For example, where denotes the -fold connected sum.
2.2 The general non-spin case
For the non-spin case we construct only those manifolds which are boundaries of -manifolds. As in the spin case, the construction depends a priori on choices, but Theorem 4.3 entails that these choices do not affect the diffeomorphism type of the manifold constructed.
Let be a pair with a surjective homomorphism and as above. We shall construct a non-spin 5-manifold with and second Stiefel-Whitney class given by composed with the projection .
If let be the non-trivial -bundle over with boundary . If let be the boundary connected sum with boundary .
In the general case, present where is an injective homomorphism between free abelian groups. Lift to and observe that there is a canonical identification . If is a basis for note that each is represented by an embedded 2-sphere with trivial normal bundle. Let be the manifold obtained by attaching 3-handles to along spheres representing and let . One may check that is a non-spin manifold as described above.
3 Invariants
Tex syntax error:
-
Tex syntax error
be the second integral homology group ofTex syntax error
, - , the homomorphism defined by evaluation with the second Stiefel-Whitney class of
Tex syntax error
, , - , the smallest extended natural number such that for some . If
Tex syntax error
is spinable we set .
For example, the manifold has invariants , non-trivial and . The Wu-manifold, , has invariants , non-trivial and .
The above list is the minimal list of invariants required to give the classification of closed simply-connected -manifolds: see Theorem 4.2 below.
In addition we mention two further invariants ofTex syntax error:
- , the third Stiefel-Whitney class,
- , the linking form of
Tex syntax error
which is a non-singular anti-symmetric bi-linear pairing on , the torsion subgroup ofTex syntax error
.
By [Milnor&Stasheff1974, Problem 8-A], , and so determines .
By [Wall1962, Proposition 1 & 2], the linking form satisfies the identity where we regard as an element of . The classification of anti-symmetric linking forms is rather simple and this leads to the fact that one only needs to list the extended natural number in order to obtain a complete list of invariants of simply-connected -manifolds: This point is clarified in the following sub-section where we report on the classification of anti-symmetric linking forms.
3.1 Linking forms
An abstract non-singular anti-symmetric linking form on a finite abelian group is a bi-linear function
Tex syntax error
Tex syntax errorfor all
Tex syntax errorif and only if
Tex syntax errorand
Tex syntax errorfor all pairs and . For example, if denotes the cyclic group of order , we have the following linking forms specified by their linking matricies,
Tex syntax error
Tex syntax error
Tex syntax error
Tex syntax erroris the sum of cyclic groups we shall write
Tex syntax errorfor the sum
Tex syntax error.
By [Wall1963, Theorem 3], all non-singular anti-symmetric linking forms are isomorphic to a sum of the linking forms above and indeed such linking forms are classified up to isomorphism by the homomorphism
Tex syntax error
Tex syntax erroror
Tex syntax errorfor some finite group with
Tex syntax errorif generates the summand. In particular the second Stiefel-Whitney class of a 5-manifold
Tex syntax errordetermines the isomorphism class of the linking form
Tex syntax errorand we see that the torsion subgroup of
Tex syntax erroris of the form
Tex syntax errorif
Tex syntax erroror
Tex syntax errorif
Tex syntax errorin which case the summand is an orthogonal summand of
Tex syntax error.
3.2 Values for constructions
Tex syntax errorall have vanishing of course and so by Wall's classification of linking forms we see that the linking form of
Tex syntax erroris the linking form .
As we mentioned above, the non-spin manifolds have given by projecting to and then applying :
If has height finite height then it follows from Wall's classification of linking forms that where and if has infinite height then .
4 Classification
We first present the most economical classifications of and . Let be the set of isomorphism classes finitely generated abelian groups with torsion subgroup where is trivial or and write and for the obvious subsets of .
Theorem 4.2 [Barden1965]. The mapping
is an injection onto the subset of pairs where if and only if .
The above theorems follow from the following theorem of Barden and the classification of anti-symmetric linking forms.
Theorem 4.3 [Barden1965, Theorem 2.2]. Let and be simply-connected, closed, smooth 5-manifolds and let be an isomorphism preserving the linking form and the second Stiefel-Whitney class. Then is realised by a diffeomorphism .
This theorem can re-phrased in categorical language as follows.
- Let be the groupoid with objects where is a finitely generated abelian group, is an anti-symmetric non-singular linking form and is a homomorphism such that for all . The morphisms of are isomorphisms of abelian groups commuting with both and .
- Let be the groupoid with objects simply-connected closed smooth -manifolds embedded in some fixed for large and morphisms isotopy classes of diffeomorphisms.
- Consider the functor
Theorem 4.4 [Barden1965]. The functor is a detecting functor. That is, it induces a bijection on isomorphism classes of objects.
4.1 Enumeration
We first give Barden's enumeration of the set , [Barden1965, Theorem 2.3].
- , , , .
- For , is the spin manifold with constructed above.
- For let constructed above be the non-spin manifold with .
With this notation [Barden1965, Theorem 2.3] states that a complete list of diffeomorphism classes of simply-connected 5-manifolds is given by
where , , divides or and denotes the connected sum of oriented manifolds. The manifold is diffeomorphic to if and only if .
An alternative complete enumeration is obtained by writing as a disjoint union
5 Further discussion
- As the invariants which classify simply-connected closed oriented 5-manifolds are homotopy invariants, we see that the same classification holds up to homotopy, homeomorphism and piecewise linear homeomorphism.
- By the construction above every simply-connected closed smooth spinable -manifold embeds into .
- As the invariants for are isomorphic to the invariants of
Tex syntax error
we see that every smooth 5-manifold admits an orientation reversing diffeomorphism: i.e. all 5-manifolds are smoothly amphicheiral.
- Barden's results have been nicely discussed and re-proven by Zhubr [Zhubr2001].
5.1 Bordism groups
Tex syntax errorand
Tex syntax erroradmits a unique spin structure which extends to
Tex syntax errorwe see that every closed spin 5-manifold bounds a spin 6-manifold. Hence the bordism group vanishes. The bordism group
Tex syntax erroris isomorphic to , see for example [Milnor&Stasheff1974, p 203]. Moreover this bordism group is detected by the Stiefel-Whitney number
Tex syntax error. The Wu-manifold has cohomology groups
Tex syntax error
Tex syntax error. It follows that
Tex syntax errorand so we have that
Tex syntax error. We see that
Tex syntax erroris the generator of
Tex syntax errorand that a closed, smooth simply-connected 5-manifold
Tex syntax erroris not a boundary if and only if it is diffeomorphic to
Tex syntax errorwhere is a Spin manifold.
5.2 Curvature and contact structures
Every manifold admits a metric of positive Ricci curvature by [Boyer&Galicki2006].
The following theorem is an immediate consequence of [Geiges1991, Theorem 1 & Lemma 7].
Theorem 5.1 [Geiges1991].
A simply connected -manifoldTex syntax erroradmits a contact structure if and only if has an integral lift in . Hence
Tex syntax erroradmits a contact structure if and only if or ; equivalently
Tex syntax erroradmits a contact structure if and only if or where .
Remark 5.2. The special case of this theorem for spin 5-manifolds with the order of prime to 3 was proven in [Thomas1986].
5.3 Mapping class groups
Tex syntax errorpreserving the linking form and the second Stiefel-Whitney class. Applying Theorem 4.3 above we obtain the following exact sequence
where is the group of isotopy classes of diffeomorphisms inducing the identity on .
- There is an isomphorism . By [Cerf1970] and [Smale1962a], , the group of homotopy -spheres. But by [Kervaire&Milnor1963], .
- In the homotopy category, , the group of homotopy classes of orientation preserving homotopy equivalences of
Tex syntax error
, has been extensively investigated by [Baues&Buth1996] and is already seen to be relatively complex. - Open problem: as of writing there is no computation of for a general simply-connected 5-manifold in the literature.
- However if has no -torsion and no -torsion then was computed in [Fang1993]. This computation agrees with a more recent conjectured answer: please see the discussion page.
- Even the computation of still leaves an unsolved extension problem in (1) above.
6 References
- [Barden1965] D. Barden, Simply connected five-manifolds, Ann. of Math. (2) 82 (1965), 365–385. MR0184241 (32 #1714) Zbl 0136.20602
- [Baues&Buth1996] H. J. Baues and J. Buth, On the group of homotopy equivalences of simply connected five manifolds, Math. Z. 222 (1996), no.4, 573–614. MR1406269 (97g:55009) Zbl 0881.55008
- [Boyer&Galicki2006] C. P. Boyer and K. Galicki, Highly connected manifolds with positive Ricci curvature, Geom. Topol. 10 (2006), 2219–2235 (electronic). MR2284055 (2007k:53057) Zbl 1129.53026
- [Cerf1970] J. Cerf, La stratification naturelle des espaces de fonctions différentiables réelles et le théorème de la pseudo-isotopie, Inst. Hautes Études Sci. Publ. Math. (1970), no.39, 5–173. MR0292089 (45 #1176) Zbl 0213.25202
- [Fang1993] F. Fang, Diffeomorphism groups of simply connected 5-manifolds, unpublished pre-print (1993).
- [Geiges1991] H. Geiges, Contact structures on -connected -manifolds, Mathematika 38 (1991), no.2, 303–311 (1992). MR1147828 (93e:57042) Zbl 0724.57017
- [Kervaire&Milnor1963] M. A. Kervaire and J. W. Milnor, Groups of homotopy spheres. I, Ann. of Math. (2) 77 (1963), 504–537. MR0148075 (26 #5584) Zbl 0115.40505
- [Milnor&Stasheff1974] J. W. Milnor and J. D. Stasheff, Characteristic classes, Princeton University Press, Princeton, N. J., 1974. MR0440554 (55 #13428) Zbl 1079.57504
- [Smale1962] S. Smale, On the structure of -manifolds, Ann. of Math. (2) 75 (1962), 38–46. MR0141133 (25 #4544) Zbl 0101.16103
- [Smale1962a] S. Smale, On the structure of manifolds, Amer. J. Math. 84 (1962), 387–399. MR0153022 (27 #2991) Zbl 0109.41103
- [Stöcker1982] R. Stöcker, On the structure of -dimensional Poincaré duality spaces, Comment. Math. Helv. 57 (1982), no.3, 481–510. MR689075 (85b:57022) Zbl 0507.57012
- [Thomas1986] C. B. Thomas, Contact structures on -connected -manifolds, 18 (1986), 255–270. MR925869 (89b:53074) Zbl 0642.57014
- [Wall1962] C. T. C. Wall, Killing the middle homotopy groups of odd dimensional manifolds, Trans. Amer. Math. Soc. 103 (1962), 421–433. MR0139185 (25 #2621) Zbl 0199.26803
- [Wall1963] C. T. C. Wall, Quadratic forms on finite groups, and related topics, Topology 2 (1963), 281–298. MR0156890 (28 #133) Zbl 0215.39903
- [Wall1964] C. T. C. Wall, Diffeomorphisms of -manifolds, J. London Math. Soc. 39 (1964), 131–140. MR0163323 (29 #626) Zbl 0121.18101
- [Zhubr2001] A. V. Zhubr, On a paper of Barden, Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 279 (2001), Geom. i Topol. 6, 70–88, 247; translation in J. Math. Sci. (N. Y.) 119 (2004), no. 1, 35–44. MR1846073 (2002e:57040) Zbl 1072.57024
7 External links
- The Wikipedia page on 1-connected 5-manifolds
Tex syntax errorand let
Tex syntax errorbe the subset of diffeomorphism classes of spinable manifolds. The calculation of
Tex syntax errorwas first obtained by Smale [Smale1962] and was one of the first applications of the h-cobordism theorem. A little latter Barden [Barden1965] devised an elegant surgery argument and applied results of [Wall1964] on the diffeomorphism groups of 4-manifolds to give an explicit and complete classification of all of
Tex syntax error.
Simply-connected 5-manifolds are an appealing class of manifolds: the dimension is just large enough so that the full power of surgery techniques can be applied but it is low enough that the manifolds are simple enough to be readily classified. A feature of simply-connected 5-manifolds is that the homotopy, homeomorphism and diffeomorphism classification all coincide. Note that not every simply-connected 5-dimensional Poincaré space is smoothable. The classification of simply-connected 5-dimensional Poincaré spaces was achieved by Stöcker [Stöcker1982].
2 Constructions and examples
We first list some familiar 5-manifolds using Barden's notation:
- .
- .
- , the total space of the non-trivial -bundle over .
- , the Wu-manifold, is the homogeneous space obtained from the standard inclusion of .
In [Barden1965, Section 1] a construction of simply-connected 5-manifolds is given by expressing them as twisted doubles where is a certain simply connected -manifold with boundary a simply-connected -manifold and is a diffeomorphism. Barden used results of [Wall1964] to show that diffeomorphisms realising the required ismorphisms of exist.
2.1 The general spin case
Next we present a construction of simply-connected spin 5-manifolds. A priori the construction depends upon choices, but applying Theorem 4.3 below shows that the choices do not affect the diffeomorphism type of the manifold constructed. Note that all homology groups are with integer coefficients.
Given a finitely generated abelian group , let denote the degree 2 Moore space with . The space may be realised as a finite CW-complex with only -cells and -cells and so there is an embedding . LetTex syntax errorbe a regular neighbourhood of and let
Tex syntax errorbe the boundary of
Tex syntax error. Then
Tex syntax erroris a closed, smooth, simply-connected, spinable 5-manifold with where is the torsion subgroup of . For example, where denotes the -fold connected sum.
2.2 The general non-spin case
For the non-spin case we construct only those manifolds which are boundaries of -manifolds. As in the spin case, the construction depends a priori on choices, but Theorem 4.3 entails that these choices do not affect the diffeomorphism type of the manifold constructed.
Let be a pair with a surjective homomorphism and as above. We shall construct a non-spin 5-manifold with and second Stiefel-Whitney class given by composed with the projection .
If let be the non-trivial -bundle over with boundary . If let be the boundary connected sum with boundary .
In the general case, present where is an injective homomorphism between free abelian groups. Lift to and observe that there is a canonical identification . If is a basis for note that each is represented by an embedded 2-sphere with trivial normal bundle. Let be the manifold obtained by attaching 3-handles to along spheres representing and let . One may check that is a non-spin manifold as described above.
3 Invariants
Tex syntax error:
-
Tex syntax error
be the second integral homology group ofTex syntax error
, - , the homomorphism defined by evaluation with the second Stiefel-Whitney class of
Tex syntax error
, , - , the smallest extended natural number such that for some . If
Tex syntax error
is spinable we set .
For example, the manifold has invariants , non-trivial and . The Wu-manifold, , has invariants , non-trivial and .
The above list is the minimal list of invariants required to give the classification of closed simply-connected -manifolds: see Theorem 4.2 below.
In addition we mention two further invariants ofTex syntax error:
- , the third Stiefel-Whitney class,
- , the linking form of
Tex syntax error
which is a non-singular anti-symmetric bi-linear pairing on , the torsion subgroup ofTex syntax error
.
By [Milnor&Stasheff1974, Problem 8-A], , and so determines .
By [Wall1962, Proposition 1 & 2], the linking form satisfies the identity where we regard as an element of . The classification of anti-symmetric linking forms is rather simple and this leads to the fact that one only needs to list the extended natural number in order to obtain a complete list of invariants of simply-connected -manifolds: This point is clarified in the following sub-section where we report on the classification of anti-symmetric linking forms.
3.1 Linking forms
An abstract non-singular anti-symmetric linking form on a finite abelian group is a bi-linear function
Tex syntax error
Tex syntax errorfor all
Tex syntax errorif and only if
Tex syntax errorand
Tex syntax errorfor all pairs and . For example, if denotes the cyclic group of order , we have the following linking forms specified by their linking matricies,
Tex syntax error
Tex syntax error
Tex syntax error
Tex syntax erroris the sum of cyclic groups we shall write
Tex syntax errorfor the sum
Tex syntax error.
By [Wall1963, Theorem 3], all non-singular anti-symmetric linking forms are isomorphic to a sum of the linking forms above and indeed such linking forms are classified up to isomorphism by the homomorphism
Tex syntax error
Tex syntax erroror
Tex syntax errorfor some finite group with
Tex syntax errorif generates the summand. In particular the second Stiefel-Whitney class of a 5-manifold
Tex syntax errordetermines the isomorphism class of the linking form
Tex syntax errorand we see that the torsion subgroup of
Tex syntax erroris of the form
Tex syntax errorif
Tex syntax erroror
Tex syntax errorif
Tex syntax errorin which case the summand is an orthogonal summand of
Tex syntax error.
3.2 Values for constructions
Tex syntax errorall have vanishing of course and so by Wall's classification of linking forms we see that the linking form of
Tex syntax erroris the linking form .
As we mentioned above, the non-spin manifolds have given by projecting to and then applying :
If has height finite height then it follows from Wall's classification of linking forms that where and if has infinite height then .
4 Classification
We first present the most economical classifications of and . Let be the set of isomorphism classes finitely generated abelian groups with torsion subgroup where is trivial or and write and for the obvious subsets of .
Theorem 4.2 [Barden1965]. The mapping
is an injection onto the subset of pairs where if and only if .
The above theorems follow from the following theorem of Barden and the classification of anti-symmetric linking forms.
Theorem 4.3 [Barden1965, Theorem 2.2]. Let and be simply-connected, closed, smooth 5-manifolds and let be an isomorphism preserving the linking form and the second Stiefel-Whitney class. Then is realised by a diffeomorphism .
This theorem can re-phrased in categorical language as follows.
- Let be the groupoid with objects where is a finitely generated abelian group, is an anti-symmetric non-singular linking form and is a homomorphism such that for all . The morphisms of are isomorphisms of abelian groups commuting with both and .
- Let be the groupoid with objects simply-connected closed smooth -manifolds embedded in some fixed for large and morphisms isotopy classes of diffeomorphisms.
- Consider the functor
Theorem 4.4 [Barden1965]. The functor is a detecting functor. That is, it induces a bijection on isomorphism classes of objects.
4.1 Enumeration
We first give Barden's enumeration of the set , [Barden1965, Theorem 2.3].
- , , , .
- For , is the spin manifold with constructed above.
- For let constructed above be the non-spin manifold with .
With this notation [Barden1965, Theorem 2.3] states that a complete list of diffeomorphism classes of simply-connected 5-manifolds is given by
where , , divides or and denotes the connected sum of oriented manifolds. The manifold is diffeomorphic to if and only if .
An alternative complete enumeration is obtained by writing as a disjoint union
5 Further discussion
- As the invariants which classify simply-connected closed oriented 5-manifolds are homotopy invariants, we see that the same classification holds up to homotopy, homeomorphism and piecewise linear homeomorphism.
- By the construction above every simply-connected closed smooth spinable -manifold embeds into .
- As the invariants for are isomorphic to the invariants of
Tex syntax error
we see that every smooth 5-manifold admits an orientation reversing diffeomorphism: i.e. all 5-manifolds are smoothly amphicheiral.
- Barden's results have been nicely discussed and re-proven by Zhubr [Zhubr2001].
5.1 Bordism groups
Tex syntax errorand
Tex syntax erroradmits a unique spin structure which extends to
Tex syntax errorwe see that every closed spin 5-manifold bounds a spin 6-manifold. Hence the bordism group vanishes. The bordism group
Tex syntax erroris isomorphic to , see for example [Milnor&Stasheff1974, p 203]. Moreover this bordism group is detected by the Stiefel-Whitney number
Tex syntax error. The Wu-manifold has cohomology groups
Tex syntax error
Tex syntax error. It follows that
Tex syntax errorand so we have that
Tex syntax error. We see that
Tex syntax erroris the generator of
Tex syntax errorand that a closed, smooth simply-connected 5-manifold
Tex syntax erroris not a boundary if and only if it is diffeomorphic to
Tex syntax errorwhere is a Spin manifold.
5.2 Curvature and contact structures
Every manifold admits a metric of positive Ricci curvature by [Boyer&Galicki2006].
The following theorem is an immediate consequence of [Geiges1991, Theorem 1 & Lemma 7].
Theorem 5.1 [Geiges1991].
A simply connected -manifoldTex syntax erroradmits a contact structure if and only if has an integral lift in . Hence
Tex syntax erroradmits a contact structure if and only if or ; equivalently
Tex syntax erroradmits a contact structure if and only if or where .
Remark 5.2. The special case of this theorem for spin 5-manifolds with the order of prime to 3 was proven in [Thomas1986].
5.3 Mapping class groups
Tex syntax errorpreserving the linking form and the second Stiefel-Whitney class. Applying Theorem 4.3 above we obtain the following exact sequence
where is the group of isotopy classes of diffeomorphisms inducing the identity on .
- There is an isomphorism . By [Cerf1970] and [Smale1962a], , the group of homotopy -spheres. But by [Kervaire&Milnor1963], .
- In the homotopy category, , the group of homotopy classes of orientation preserving homotopy equivalences of
Tex syntax error
, has been extensively investigated by [Baues&Buth1996] and is already seen to be relatively complex. - Open problem: as of writing there is no computation of for a general simply-connected 5-manifold in the literature.
- However if has no -torsion and no -torsion then was computed in [Fang1993]. This computation agrees with a more recent conjectured answer: please see the discussion page.
- Even the computation of still leaves an unsolved extension problem in (1) above.
6 References
- [Barden1965] D. Barden, Simply connected five-manifolds, Ann. of Math. (2) 82 (1965), 365–385. MR0184241 (32 #1714) Zbl 0136.20602
- [Baues&Buth1996] H. J. Baues and J. Buth, On the group of homotopy equivalences of simply connected five manifolds, Math. Z. 222 (1996), no.4, 573–614. MR1406269 (97g:55009) Zbl 0881.55008
- [Boyer&Galicki2006] C. P. Boyer and K. Galicki, Highly connected manifolds with positive Ricci curvature, Geom. Topol. 10 (2006), 2219–2235 (electronic). MR2284055 (2007k:53057) Zbl 1129.53026
- [Cerf1970] J. Cerf, La stratification naturelle des espaces de fonctions différentiables réelles et le théorème de la pseudo-isotopie, Inst. Hautes Études Sci. Publ. Math. (1970), no.39, 5–173. MR0292089 (45 #1176) Zbl 0213.25202
- [Fang1993] F. Fang, Diffeomorphism groups of simply connected 5-manifolds, unpublished pre-print (1993).
- [Geiges1991] H. Geiges, Contact structures on -connected -manifolds, Mathematika 38 (1991), no.2, 303–311 (1992). MR1147828 (93e:57042) Zbl 0724.57017
- [Kervaire&Milnor1963] M. A. Kervaire and J. W. Milnor, Groups of homotopy spheres. I, Ann. of Math. (2) 77 (1963), 504–537. MR0148075 (26 #5584) Zbl 0115.40505
- [Milnor&Stasheff1974] J. W. Milnor and J. D. Stasheff, Characteristic classes, Princeton University Press, Princeton, N. J., 1974. MR0440554 (55 #13428) Zbl 1079.57504
- [Smale1962] S. Smale, On the structure of -manifolds, Ann. of Math. (2) 75 (1962), 38–46. MR0141133 (25 #4544) Zbl 0101.16103
- [Smale1962a] S. Smale, On the structure of manifolds, Amer. J. Math. 84 (1962), 387–399. MR0153022 (27 #2991) Zbl 0109.41103
- [Stöcker1982] R. Stöcker, On the structure of -dimensional Poincaré duality spaces, Comment. Math. Helv. 57 (1982), no.3, 481–510. MR689075 (85b:57022) Zbl 0507.57012
- [Thomas1986] C. B. Thomas, Contact structures on -connected -manifolds, 18 (1986), 255–270. MR925869 (89b:53074) Zbl 0642.57014
- [Wall1962] C. T. C. Wall, Killing the middle homotopy groups of odd dimensional manifolds, Trans. Amer. Math. Soc. 103 (1962), 421–433. MR0139185 (25 #2621) Zbl 0199.26803
- [Wall1963] C. T. C. Wall, Quadratic forms on finite groups, and related topics, Topology 2 (1963), 281–298. MR0156890 (28 #133) Zbl 0215.39903
- [Wall1964] C. T. C. Wall, Diffeomorphisms of -manifolds, J. London Math. Soc. 39 (1964), 131–140. MR0163323 (29 #626) Zbl 0121.18101
- [Zhubr2001] A. V. Zhubr, On a paper of Barden, Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 279 (2001), Geom. i Topol. 6, 70–88, 247; translation in J. Math. Sci. (N. Y.) 119 (2004), no. 1, 35–44. MR1846073 (2002e:57040) Zbl 1072.57024
7 External links
- The Wikipedia page on 1-connected 5-manifolds
Tex syntax errorand let
Tex syntax errorbe the subset of diffeomorphism classes of spinable manifolds. The calculation of
Tex syntax errorwas first obtained by Smale [Smale1962] and was one of the first applications of the h-cobordism theorem. A little latter Barden [Barden1965] devised an elegant surgery argument and applied results of [Wall1964] on the diffeomorphism groups of 4-manifolds to give an explicit and complete classification of all of
Tex syntax error.
Simply-connected 5-manifolds are an appealing class of manifolds: the dimension is just large enough so that the full power of surgery techniques can be applied but it is low enough that the manifolds are simple enough to be readily classified. A feature of simply-connected 5-manifolds is that the homotopy, homeomorphism and diffeomorphism classification all coincide. Note that not every simply-connected 5-dimensional Poincaré space is smoothable. The classification of simply-connected 5-dimensional Poincaré spaces was achieved by Stöcker [Stöcker1982].
2 Constructions and examples
We first list some familiar 5-manifolds using Barden's notation:
- .
- .
- , the total space of the non-trivial -bundle over .
- , the Wu-manifold, is the homogeneous space obtained from the standard inclusion of .
In [Barden1965, Section 1] a construction of simply-connected 5-manifolds is given by expressing them as twisted doubles where is a certain simply connected -manifold with boundary a simply-connected -manifold and is a diffeomorphism. Barden used results of [Wall1964] to show that diffeomorphisms realising the required ismorphisms of exist.
2.1 The general spin case
Next we present a construction of simply-connected spin 5-manifolds. A priori the construction depends upon choices, but applying Theorem 4.3 below shows that the choices do not affect the diffeomorphism type of the manifold constructed. Note that all homology groups are with integer coefficients.
Given a finitely generated abelian group , let denote the degree 2 Moore space with . The space may be realised as a finite CW-complex with only -cells and -cells and so there is an embedding . LetTex syntax errorbe a regular neighbourhood of and let
Tex syntax errorbe the boundary of
Tex syntax error. Then
Tex syntax erroris a closed, smooth, simply-connected, spinable 5-manifold with where is the torsion subgroup of . For example, where denotes the -fold connected sum.
2.2 The general non-spin case
For the non-spin case we construct only those manifolds which are boundaries of -manifolds. As in the spin case, the construction depends a priori on choices, but Theorem 4.3 entails that these choices do not affect the diffeomorphism type of the manifold constructed.
Let be a pair with a surjective homomorphism and as above. We shall construct a non-spin 5-manifold with and second Stiefel-Whitney class given by composed with the projection .
If let be the non-trivial -bundle over with boundary . If let be the boundary connected sum with boundary .
In the general case, present where is an injective homomorphism between free abelian groups. Lift to and observe that there is a canonical identification . If is a basis for note that each is represented by an embedded 2-sphere with trivial normal bundle. Let be the manifold obtained by attaching 3-handles to along spheres representing and let . One may check that is a non-spin manifold as described above.
3 Invariants
Tex syntax error:
-
Tex syntax error
be the second integral homology group ofTex syntax error
, - , the homomorphism defined by evaluation with the second Stiefel-Whitney class of
Tex syntax error
, , - , the smallest extended natural number such that for some . If
Tex syntax error
is spinable we set .
For example, the manifold has invariants , non-trivial and . The Wu-manifold, , has invariants , non-trivial and .
The above list is the minimal list of invariants required to give the classification of closed simply-connected -manifolds: see Theorem 4.2 below.
In addition we mention two further invariants ofTex syntax error:
- , the third Stiefel-Whitney class,
- , the linking form of
Tex syntax error
which is a non-singular anti-symmetric bi-linear pairing on , the torsion subgroup ofTex syntax error
.
By [Milnor&Stasheff1974, Problem 8-A], , and so determines .
By [Wall1962, Proposition 1 & 2], the linking form satisfies the identity where we regard as an element of . The classification of anti-symmetric linking forms is rather simple and this leads to the fact that one only needs to list the extended natural number in order to obtain a complete list of invariants of simply-connected -manifolds: This point is clarified in the following sub-section where we report on the classification of anti-symmetric linking forms.
3.1 Linking forms
An abstract non-singular anti-symmetric linking form on a finite abelian group is a bi-linear function
Tex syntax error
Tex syntax errorfor all
Tex syntax errorif and only if
Tex syntax errorand
Tex syntax errorfor all pairs and . For example, if denotes the cyclic group of order , we have the following linking forms specified by their linking matricies,
Tex syntax error
Tex syntax error
Tex syntax error
Tex syntax erroris the sum of cyclic groups we shall write
Tex syntax errorfor the sum
Tex syntax error.
By [Wall1963, Theorem 3], all non-singular anti-symmetric linking forms are isomorphic to a sum of the linking forms above and indeed such linking forms are classified up to isomorphism by the homomorphism
Tex syntax error
Tex syntax erroror
Tex syntax errorfor some finite group with
Tex syntax errorif generates the summand. In particular the second Stiefel-Whitney class of a 5-manifold
Tex syntax errordetermines the isomorphism class of the linking form
Tex syntax errorand we see that the torsion subgroup of
Tex syntax erroris of the form
Tex syntax errorif
Tex syntax erroror
Tex syntax errorif
Tex syntax errorin which case the summand is an orthogonal summand of
Tex syntax error.
3.2 Values for constructions
Tex syntax errorall have vanishing of course and so by Wall's classification of linking forms we see that the linking form of
Tex syntax erroris the linking form .
As we mentioned above, the non-spin manifolds have given by projecting to and then applying :
If has height finite height then it follows from Wall's classification of linking forms that where and if has infinite height then .
4 Classification
We first present the most economical classifications of and . Let be the set of isomorphism classes finitely generated abelian groups with torsion subgroup where is trivial or and write and for the obvious subsets of .
Theorem 4.2 [Barden1965]. The mapping
is an injection onto the subset of pairs where if and only if .
The above theorems follow from the following theorem of Barden and the classification of anti-symmetric linking forms.
Theorem 4.3 [Barden1965, Theorem 2.2]. Let and be simply-connected, closed, smooth 5-manifolds and let be an isomorphism preserving the linking form and the second Stiefel-Whitney class. Then is realised by a diffeomorphism .
This theorem can re-phrased in categorical language as follows.
- Let be the groupoid with objects where is a finitely generated abelian group, is an anti-symmetric non-singular linking form and is a homomorphism such that for all . The morphisms of are isomorphisms of abelian groups commuting with both and .
- Let be the groupoid with objects simply-connected closed smooth -manifolds embedded in some fixed for large and morphisms isotopy classes of diffeomorphisms.
- Consider the functor
Theorem 4.4 [Barden1965]. The functor is a detecting functor. That is, it induces a bijection on isomorphism classes of objects.
4.1 Enumeration
We first give Barden's enumeration of the set , [Barden1965, Theorem 2.3].
- , , , .
- For , is the spin manifold with constructed above.
- For let constructed above be the non-spin manifold with .
With this notation [Barden1965, Theorem 2.3] states that a complete list of diffeomorphism classes of simply-connected 5-manifolds is given by
where , , divides or and denotes the connected sum of oriented manifolds. The manifold is diffeomorphic to if and only if .
An alternative complete enumeration is obtained by writing as a disjoint union
5 Further discussion
- As the invariants which classify simply-connected closed oriented 5-manifolds are homotopy invariants, we see that the same classification holds up to homotopy, homeomorphism and piecewise linear homeomorphism.
- By the construction above every simply-connected closed smooth spinable -manifold embeds into .
- As the invariants for are isomorphic to the invariants of
Tex syntax error
we see that every smooth 5-manifold admits an orientation reversing diffeomorphism: i.e. all 5-manifolds are smoothly amphicheiral.
- Barden's results have been nicely discussed and re-proven by Zhubr [Zhubr2001].
5.1 Bordism groups
Tex syntax errorand
Tex syntax erroradmits a unique spin structure which extends to
Tex syntax errorwe see that every closed spin 5-manifold bounds a spin 6-manifold. Hence the bordism group vanishes. The bordism group
Tex syntax erroris isomorphic to , see for example [Milnor&Stasheff1974, p 203]. Moreover this bordism group is detected by the Stiefel-Whitney number
Tex syntax error. The Wu-manifold has cohomology groups
Tex syntax error
Tex syntax error. It follows that
Tex syntax errorand so we have that
Tex syntax error. We see that
Tex syntax erroris the generator of
Tex syntax errorand that a closed, smooth simply-connected 5-manifold
Tex syntax erroris not a boundary if and only if it is diffeomorphic to
Tex syntax errorwhere is a Spin manifold.
5.2 Curvature and contact structures
Every manifold admits a metric of positive Ricci curvature by [Boyer&Galicki2006].
The following theorem is an immediate consequence of [Geiges1991, Theorem 1 & Lemma 7].
Theorem 5.1 [Geiges1991].
A simply connected -manifoldTex syntax erroradmits a contact structure if and only if has an integral lift in . Hence
Tex syntax erroradmits a contact structure if and only if or ; equivalently
Tex syntax erroradmits a contact structure if and only if or where .
Remark 5.2. The special case of this theorem for spin 5-manifolds with the order of prime to 3 was proven in [Thomas1986].
5.3 Mapping class groups
Tex syntax errorpreserving the linking form and the second Stiefel-Whitney class. Applying Theorem 4.3 above we obtain the following exact sequence
where is the group of isotopy classes of diffeomorphisms inducing the identity on .
- There is an isomphorism . By [Cerf1970] and [Smale1962a], , the group of homotopy -spheres. But by [Kervaire&Milnor1963], .
- In the homotopy category, , the group of homotopy classes of orientation preserving homotopy equivalences of
Tex syntax error
, has been extensively investigated by [Baues&Buth1996] and is already seen to be relatively complex. - Open problem: as of writing there is no computation of for a general simply-connected 5-manifold in the literature.
- However if has no -torsion and no -torsion then was computed in [Fang1993]. This computation agrees with a more recent conjectured answer: please see the discussion page.
- Even the computation of still leaves an unsolved extension problem in (1) above.
6 References
- [Barden1965] D. Barden, Simply connected five-manifolds, Ann. of Math. (2) 82 (1965), 365–385. MR0184241 (32 #1714) Zbl 0136.20602
- [Baues&Buth1996] H. J. Baues and J. Buth, On the group of homotopy equivalences of simply connected five manifolds, Math. Z. 222 (1996), no.4, 573–614. MR1406269 (97g:55009) Zbl 0881.55008
- [Boyer&Galicki2006] C. P. Boyer and K. Galicki, Highly connected manifolds with positive Ricci curvature, Geom. Topol. 10 (2006), 2219–2235 (electronic). MR2284055 (2007k:53057) Zbl 1129.53026
- [Cerf1970] J. Cerf, La stratification naturelle des espaces de fonctions différentiables réelles et le théorème de la pseudo-isotopie, Inst. Hautes Études Sci. Publ. Math. (1970), no.39, 5–173. MR0292089 (45 #1176) Zbl 0213.25202
- [Fang1993] F. Fang, Diffeomorphism groups of simply connected 5-manifolds, unpublished pre-print (1993).
- [Geiges1991] H. Geiges, Contact structures on -connected -manifolds, Mathematika 38 (1991), no.2, 303–311 (1992). MR1147828 (93e:57042) Zbl 0724.57017
- [Kervaire&Milnor1963] M. A. Kervaire and J. W. Milnor, Groups of homotopy spheres. I, Ann. of Math. (2) 77 (1963), 504–537. MR0148075 (26 #5584) Zbl 0115.40505
- [Milnor&Stasheff1974] J. W. Milnor and J. D. Stasheff, Characteristic classes, Princeton University Press, Princeton, N. J., 1974. MR0440554 (55 #13428) Zbl 1079.57504
- [Smale1962] S. Smale, On the structure of -manifolds, Ann. of Math. (2) 75 (1962), 38–46. MR0141133 (25 #4544) Zbl 0101.16103
- [Smale1962a] S. Smale, On the structure of manifolds, Amer. J. Math. 84 (1962), 387–399. MR0153022 (27 #2991) Zbl 0109.41103
- [Stöcker1982] R. Stöcker, On the structure of -dimensional Poincaré duality spaces, Comment. Math. Helv. 57 (1982), no.3, 481–510. MR689075 (85b:57022) Zbl 0507.57012
- [Thomas1986] C. B. Thomas, Contact structures on -connected -manifolds, 18 (1986), 255–270. MR925869 (89b:53074) Zbl 0642.57014
- [Wall1962] C. T. C. Wall, Killing the middle homotopy groups of odd dimensional manifolds, Trans. Amer. Math. Soc. 103 (1962), 421–433. MR0139185 (25 #2621) Zbl 0199.26803
- [Wall1963] C. T. C. Wall, Quadratic forms on finite groups, and related topics, Topology 2 (1963), 281–298. MR0156890 (28 #133) Zbl 0215.39903
- [Wall1964] C. T. C. Wall, Diffeomorphisms of -manifolds, J. London Math. Soc. 39 (1964), 131–140. MR0163323 (29 #626) Zbl 0121.18101
- [Zhubr2001] A. V. Zhubr, On a paper of Barden, Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 279 (2001), Geom. i Topol. 6, 70–88, 247; translation in J. Math. Sci. (N. Y.) 119 (2004), no. 1, 35–44. MR1846073 (2002e:57040) Zbl 1072.57024
7 External links
- The Wikipedia page on 1-connected 5-manifolds
Tex syntax errorand let
Tex syntax errorbe the subset of diffeomorphism classes of spinable manifolds. The calculation of
Tex syntax errorwas first obtained by Smale [Smale1962] and was one of the first applications of the h-cobordism theorem. A little latter Barden [Barden1965] devised an elegant surgery argument and applied results of [Wall1964] on the diffeomorphism groups of 4-manifolds to give an explicit and complete classification of all of
Tex syntax error.
Simply-connected 5-manifolds are an appealing class of manifolds: the dimension is just large enough so that the full power of surgery techniques can be applied but it is low enough that the manifolds are simple enough to be readily classified. A feature of simply-connected 5-manifolds is that the homotopy, homeomorphism and diffeomorphism classification all coincide. Note that not every simply-connected 5-dimensional Poincaré space is smoothable. The classification of simply-connected 5-dimensional Poincaré spaces was achieved by Stöcker [Stöcker1982].
2 Constructions and examples
We first list some familiar 5-manifolds using Barden's notation:
- .
- .
- , the total space of the non-trivial -bundle over .
- , the Wu-manifold, is the homogeneous space obtained from the standard inclusion of .
In [Barden1965, Section 1] a construction of simply-connected 5-manifolds is given by expressing them as twisted doubles where is a certain simply connected -manifold with boundary a simply-connected -manifold and is a diffeomorphism. Barden used results of [Wall1964] to show that diffeomorphisms realising the required ismorphisms of exist.
2.1 The general spin case
Next we present a construction of simply-connected spin 5-manifolds. A priori the construction depends upon choices, but applying Theorem 4.3 below shows that the choices do not affect the diffeomorphism type of the manifold constructed. Note that all homology groups are with integer coefficients.
Given a finitely generated abelian group , let denote the degree 2 Moore space with . The space may be realised as a finite CW-complex with only -cells and -cells and so there is an embedding . LetTex syntax errorbe a regular neighbourhood of and let
Tex syntax errorbe the boundary of
Tex syntax error. Then
Tex syntax erroris a closed, smooth, simply-connected, spinable 5-manifold with where is the torsion subgroup of . For example, where denotes the -fold connected sum.
2.2 The general non-spin case
For the non-spin case we construct only those manifolds which are boundaries of -manifolds. As in the spin case, the construction depends a priori on choices, but Theorem 4.3 entails that these choices do not affect the diffeomorphism type of the manifold constructed.
Let be a pair with a surjective homomorphism and as above. We shall construct a non-spin 5-manifold with and second Stiefel-Whitney class given by composed with the projection .
If let be the non-trivial -bundle over with boundary . If let be the boundary connected sum with boundary .
In the general case, present where is an injective homomorphism between free abelian groups. Lift to and observe that there is a canonical identification . If is a basis for note that each is represented by an embedded 2-sphere with trivial normal bundle. Let be the manifold obtained by attaching 3-handles to along spheres representing and let . One may check that is a non-spin manifold as described above.
3 Invariants
Tex syntax error:
-
Tex syntax error
be the second integral homology group ofTex syntax error
, - , the homomorphism defined by evaluation with the second Stiefel-Whitney class of
Tex syntax error
, , - , the smallest extended natural number such that for some . If
Tex syntax error
is spinable we set .
For example, the manifold has invariants , non-trivial and . The Wu-manifold, , has invariants , non-trivial and .
The above list is the minimal list of invariants required to give the classification of closed simply-connected -manifolds: see Theorem 4.2 below.
In addition we mention two further invariants ofTex syntax error:
- , the third Stiefel-Whitney class,
- , the linking form of
Tex syntax error
which is a non-singular anti-symmetric bi-linear pairing on , the torsion subgroup ofTex syntax error
.
By [Milnor&Stasheff1974, Problem 8-A], , and so determines .
By [Wall1962, Proposition 1 & 2], the linking form satisfies the identity where we regard as an element of . The classification of anti-symmetric linking forms is rather simple and this leads to the fact that one only needs to list the extended natural number in order to obtain a complete list of invariants of simply-connected -manifolds: This point is clarified in the following sub-section where we report on the classification of anti-symmetric linking forms.
3.1 Linking forms
An abstract non-singular anti-symmetric linking form on a finite abelian group is a bi-linear function
Tex syntax error
Tex syntax errorfor all
Tex syntax errorif and only if
Tex syntax errorand
Tex syntax errorfor all pairs and . For example, if denotes the cyclic group of order , we have the following linking forms specified by their linking matricies,
Tex syntax error
Tex syntax error
Tex syntax error
Tex syntax erroris the sum of cyclic groups we shall write
Tex syntax errorfor the sum
Tex syntax error.
By [Wall1963, Theorem 3], all non-singular anti-symmetric linking forms are isomorphic to a sum of the linking forms above and indeed such linking forms are classified up to isomorphism by the homomorphism
Tex syntax error
Tex syntax erroror
Tex syntax errorfor some finite group with
Tex syntax errorif generates the summand. In particular the second Stiefel-Whitney class of a 5-manifold
Tex syntax errordetermines the isomorphism class of the linking form
Tex syntax errorand we see that the torsion subgroup of
Tex syntax erroris of the form
Tex syntax errorif
Tex syntax erroror
Tex syntax errorif
Tex syntax errorin which case the summand is an orthogonal summand of
Tex syntax error.
3.2 Values for constructions
Tex syntax errorall have vanishing of course and so by Wall's classification of linking forms we see that the linking form of
Tex syntax erroris the linking form .
As we mentioned above, the non-spin manifolds have given by projecting to and then applying :
If has height finite height then it follows from Wall's classification of linking forms that where and if has infinite height then .
4 Classification
We first present the most economical classifications of and . Let be the set of isomorphism classes finitely generated abelian groups with torsion subgroup where is trivial or and write and for the obvious subsets of .
Theorem 4.2 [Barden1965]. The mapping
is an injection onto the subset of pairs where if and only if .
The above theorems follow from the following theorem of Barden and the classification of anti-symmetric linking forms.
Theorem 4.3 [Barden1965, Theorem 2.2]. Let and be simply-connected, closed, smooth 5-manifolds and let be an isomorphism preserving the linking form and the second Stiefel-Whitney class. Then is realised by a diffeomorphism .
This theorem can re-phrased in categorical language as follows.
- Let be the groupoid with objects where is a finitely generated abelian group, is an anti-symmetric non-singular linking form and is a homomorphism such that for all . The morphisms of are isomorphisms of abelian groups commuting with both and .
- Let be the groupoid with objects simply-connected closed smooth -manifolds embedded in some fixed for large and morphisms isotopy classes of diffeomorphisms.
- Consider the functor
Theorem 4.4 [Barden1965]. The functor is a detecting functor. That is, it induces a bijection on isomorphism classes of objects.
4.1 Enumeration
We first give Barden's enumeration of the set , [Barden1965, Theorem 2.3].
- , , , .
- For , is the spin manifold with constructed above.
- For let constructed above be the non-spin manifold with .
With this notation [Barden1965, Theorem 2.3] states that a complete list of diffeomorphism classes of simply-connected 5-manifolds is given by
where , , divides or and denotes the connected sum of oriented manifolds. The manifold is diffeomorphic to if and only if .
An alternative complete enumeration is obtained by writing as a disjoint union
5 Further discussion
- As the invariants which classify simply-connected closed oriented 5-manifolds are homotopy invariants, we see that the same classification holds up to homotopy, homeomorphism and piecewise linear homeomorphism.
- By the construction above every simply-connected closed smooth spinable -manifold embeds into .
- As the invariants for are isomorphic to the invariants of
Tex syntax error
we see that every smooth 5-manifold admits an orientation reversing diffeomorphism: i.e. all 5-manifolds are smoothly amphicheiral.
- Barden's results have been nicely discussed and re-proven by Zhubr [Zhubr2001].
5.1 Bordism groups
Tex syntax errorand
Tex syntax erroradmits a unique spin structure which extends to
Tex syntax errorwe see that every closed spin 5-manifold bounds a spin 6-manifold. Hence the bordism group vanishes. The bordism group
Tex syntax erroris isomorphic to , see for example [Milnor&Stasheff1974, p 203]. Moreover this bordism group is detected by the Stiefel-Whitney number
Tex syntax error. The Wu-manifold has cohomology groups
Tex syntax error
Tex syntax error. It follows that
Tex syntax errorand so we have that
Tex syntax error. We see that
Tex syntax erroris the generator of
Tex syntax errorand that a closed, smooth simply-connected 5-manifold
Tex syntax erroris not a boundary if and only if it is diffeomorphic to
Tex syntax errorwhere is a Spin manifold.
5.2 Curvature and contact structures
Every manifold admits a metric of positive Ricci curvature by [Boyer&Galicki2006].
The following theorem is an immediate consequence of [Geiges1991, Theorem 1 & Lemma 7].
Theorem 5.1 [Geiges1991].
A simply connected -manifoldTex syntax erroradmits a contact structure if and only if has an integral lift in . Hence
Tex syntax erroradmits a contact structure if and only if or ; equivalently
Tex syntax erroradmits a contact structure if and only if or where .
Remark 5.2. The special case of this theorem for spin 5-manifolds with the order of prime to 3 was proven in [Thomas1986].
5.3 Mapping class groups
Tex syntax errorpreserving the linking form and the second Stiefel-Whitney class. Applying Theorem 4.3 above we obtain the following exact sequence
where is the group of isotopy classes of diffeomorphisms inducing the identity on .
- There is an isomphorism . By [Cerf1970] and [Smale1962a], , the group of homotopy -spheres. But by [Kervaire&Milnor1963], .
- In the homotopy category, , the group of homotopy classes of orientation preserving homotopy equivalences of
Tex syntax error
, has been extensively investigated by [Baues&Buth1996] and is already seen to be relatively complex. - Open problem: as of writing there is no computation of for a general simply-connected 5-manifold in the literature.
- However if has no -torsion and no -torsion then was computed in [Fang1993]. This computation agrees with a more recent conjectured answer: please see the discussion page.
- Even the computation of still leaves an unsolved extension problem in (1) above.
6 References
- [Barden1965] D. Barden, Simply connected five-manifolds, Ann. of Math. (2) 82 (1965), 365–385. MR0184241 (32 #1714) Zbl 0136.20602
- [Baues&Buth1996] H. J. Baues and J. Buth, On the group of homotopy equivalences of simply connected five manifolds, Math. Z. 222 (1996), no.4, 573–614. MR1406269 (97g:55009) Zbl 0881.55008
- [Boyer&Galicki2006] C. P. Boyer and K. Galicki, Highly connected manifolds with positive Ricci curvature, Geom. Topol. 10 (2006), 2219–2235 (electronic). MR2284055 (2007k:53057) Zbl 1129.53026
- [Cerf1970] J. Cerf, La stratification naturelle des espaces de fonctions différentiables réelles et le théorème de la pseudo-isotopie, Inst. Hautes Études Sci. Publ. Math. (1970), no.39, 5–173. MR0292089 (45 #1176) Zbl 0213.25202
- [Fang1993] F. Fang, Diffeomorphism groups of simply connected 5-manifolds, unpublished pre-print (1993).
- [Geiges1991] H. Geiges, Contact structures on -connected -manifolds, Mathematika 38 (1991), no.2, 303–311 (1992). MR1147828 (93e:57042) Zbl 0724.57017
- [Kervaire&Milnor1963] M. A. Kervaire and J. W. Milnor, Groups of homotopy spheres. I, Ann. of Math. (2) 77 (1963), 504–537. MR0148075 (26 #5584) Zbl 0115.40505
- [Milnor&Stasheff1974] J. W. Milnor and J. D. Stasheff, Characteristic classes, Princeton University Press, Princeton, N. J., 1974. MR0440554 (55 #13428) Zbl 1079.57504
- [Smale1962] S. Smale, On the structure of -manifolds, Ann. of Math. (2) 75 (1962), 38–46. MR0141133 (25 #4544) Zbl 0101.16103
- [Smale1962a] S. Smale, On the structure of manifolds, Amer. J. Math. 84 (1962), 387–399. MR0153022 (27 #2991) Zbl 0109.41103
- [Stöcker1982] R. Stöcker, On the structure of -dimensional Poincaré duality spaces, Comment. Math. Helv. 57 (1982), no.3, 481–510. MR689075 (85b:57022) Zbl 0507.57012
- [Thomas1986] C. B. Thomas, Contact structures on -connected -manifolds, 18 (1986), 255–270. MR925869 (89b:53074) Zbl 0642.57014
- [Wall1962] C. T. C. Wall, Killing the middle homotopy groups of odd dimensional manifolds, Trans. Amer. Math. Soc. 103 (1962), 421–433. MR0139185 (25 #2621) Zbl 0199.26803
- [Wall1963] C. T. C. Wall, Quadratic forms on finite groups, and related topics, Topology 2 (1963), 281–298. MR0156890 (28 #133) Zbl 0215.39903
- [Wall1964] C. T. C. Wall, Diffeomorphisms of -manifolds, J. London Math. Soc. 39 (1964), 131–140. MR0163323 (29 #626) Zbl 0121.18101
- [Zhubr2001] A. V. Zhubr, On a paper of Barden, Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 279 (2001), Geom. i Topol. 6, 70–88, 247; translation in J. Math. Sci. (N. Y.) 119 (2004), no. 1, 35–44. MR1846073 (2002e:57040) Zbl 1072.57024
7 External links
- The Wikipedia page on 1-connected 5-manifolds