symmetric monoidal (∞,1)-category of spectra
This entry explains the J-homomorphism, states how its image is the first (chromatic) layer of the sphere spectrum; and then motivated by this explains some basic notions of chromatic homotopy theory, notably the origin of the general -Adams spectral sequence.
The J-homomorphism is a map from the homotopy groups of the stable orthogonal group (which are completely understood) to the stable homotopy groups of spheres (which in their totality are hard to compute).
For regard the -sphere (as a topological space) as the one-point compactification of the Cartesian space
Since the process of one-point compactification is a functor on proper maps, hence on homeomorphisms, via def. the -sphere inherits from the canonical action of the orthogonal group on an action
(by continuous maps) which preserves the base point (the “point at infinity”).
For definiteness we distinguish in the following notationally between
the -sphere regarded as a topological space;
its homotopy type ∞Grpd given by its fundamental ∞-groupoid.
Similarly we write for the homotopy type of the orthogonal group, regarded as a group object in an (∞,1)-category in ∞Grpd (using that the shape modality preserves finite products).
For write for the automorphism ∞-group of homotopy self-equivalences , hence
The ∞-group , def. , constitutes the two connected components of the -fold based loop space corresponding to the homotopy groups .
Via the presentation of ∞Grpd by the cartesian closed model structure on compactly generated topological spaces (and using that and and hence their product are compact) we have that for the continuous action of on of remark , which by cartesian closure is equivalently a homomorphism of topological groups of the form
induces a homomorphism of ∞-groups of the form
This in turn induces for each homomorphisms of homotopy groups of the form
By construction, the homomorphisms of remark are compatible with suspension in that for all the diagrams
in commute, and hence so do the diagrams
in , up to homotopy.
Therefore one can take the direct limit over :
By remark there is induced a homomorphism
from the homotopy groups of the stable orthogonal group to the stable homotopy groups of spheres. This is called the J-homomorphism.
Since the maps of def. are ∞-group homomorphisms, there exists their delooping
Here is the ∞-group of units of the sphere spectrum.
This map is the universal characteristic class of stable vector bundles with values in spherical fibrations:
For a vector bundle, write for its fiber-wise one-point compactification. This is a sphere bundle, a spherical fibration. Write for the -parameterized spectrum which is fiberwise the suspension spectrum of .
It is immediate that:
For a vector bundle classified by a map , the corresponding spherical fibration , def. , is classified by , def. .
Since the J-homomorphism maps from something well-understood to something hard to understand, it is of interst to characterize its image, “the image of J”.
The following characterization of the image of the J-homomorphism on homotopy groups derives from a statement that was first conjectured in (Adams 66) – and since called the Adams conjecture – and then proven in (Quillen 71, Sullivan 74).
By the discussion at orthogonal group – homotopy groups we have that the homotopy groups of the stable orthogonal group are
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
---|---|---|---|---|---|---|---|---|
0 | 0 | 0 | 0 |
Because all groups appearing here and in the following are cyclic groups, we instead write down the order
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | |
---|---|---|---|---|---|---|---|---|
2 | 2 | 1 | 1 | 1 | 1 |
For the following statement it is convenient to restrict to J-homomorphism to the stable special orthogonal group , which removes the lowest degree homotopy group in the above
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ||
---|---|---|---|---|---|---|---|---|---|
0 | 0 | 0 | 0 | 0 |
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ||
---|---|---|---|---|---|---|---|---|---|
1 | 2 | 2 | 1 | 1 | 1 | 1 |
The stable homotopy groups of spheres are the direct sum of the (cyclic) image of the J-homomorphism, def. , applied to the special orthogonal group and the kernel of the Adams e-invariant.
Moreover,
for and and positive the J-homomorphism is injective, hence its image is ,
for and hence for , the order of the image is equal to the denominator of in its reduced form, where is the Bernoulli number
for all other cases the image is necessarily zero.
The characterization of this image is due to (Adams 66, Quillen 71, Sullivan 74). Specifically the identification of is (Adams 65a, theorem 3.7 and the direct summand property is (Adams 66, theorems 1.1-1.6.). That the image is a direct summand of the codomain is proven for instance in (Switzer 75, end of chapter 19).
A modern version of the proof, using methods from chromatic homotopy theory, is surveyed in some detail in (Lorman 13).
The statement of the theorem is recalled for instance as (Ravenel, chapter 1, theorem 1.1.13). Another computation of the image of is in (Ravenel, chapter 5, section 3).
The order of in theorem is for low given by the following table
k | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
---|---|---|---|---|---|---|---|---|---|---|
24 | 240 | 504 | 480 | 264 | 65,520 | 24 | 16,320 | 28,728 | 13,200 |
See for instance (Ravenel, Chapt. 1, p. 5).
Therefore we have in low degree the following situation
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Whitehead tower of orthogonal group | orientation | spin group | string group | fivebrane group | ninebrane group | |||||||||||||
higher versions | special orthogonal group | spin group | string 2-group | fivebrane 6-group | ninebrane 10-group | |||||||||||||
homotopy groups of stable orthogonal group | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||||||||
stable homotopy groups of spheres | 0 | 0 | 0 | |||||||||||||||
image of J-homomorphism | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
The following tables show the p-primary components of the stable homotopy groups of spheres for low values, the image of J appears as the bottom row.
Here the horizontal index is the degree of the stable homotopy group . The appearance of a string of connected dots vertically above index means that there is a direct summand primary group of order . See example below for illustration. (These tables are taken from (Hatcher), where in turn they were generated based on (Ravenel 86)).
-primary component (e.g. Ravenel 86, theorem 3.2.11, figure 4.4.46)
-primary component
-primary component
We illustrate how to read these tables:
The finite abelian group decomposes into primary groups as . Here corresponds to the three dots above in the first table, and to the single dot over in the second.
The finite abelian group decomposes into primary groups as . Here corresponds to the four dots above in the first table, and to the single dot over in the second and to the single dot over in the third table.
The finite abelian group has primary group-decomposition and so this corresponds to the three connected dots over in the first table and the two connected dots over in the second (and there will be one dot over in the fourth table for not shown here).
The groups correspond to the single dots over in the first table, respectively.
The group corresponds to the two unconnected dots over in the first table.
Similarly the group corresponds to the three unconnected dots above in the first table.
The above tables, example , suggest that the image of the J-homomorphism is in some sense the “lowest order layer” of the stable homotopy groups of spheres. This is made precise by the following characterization of the image in stable homotopy theory. We bluntly state this here and give all the relevant definitions below.
Write for the first Morava E-theory spectrum at given prime number . Write for the Bousfield localization of spectra of the sphere spectrum at .
The homotopy groups of the -localized sphere spectrum are
This appears as (Lurie 10, theorem 6)
Write for the p-localization of the sphere spectrum. For , write for the image of the -localized J-homomorphism
For , the further Bousfield localization at Morava E(1)-theory induces a isomorphism
between the image of the -homomorphism and the -local stable homotopy groups of spheres.
In this form this appears as (Lurie 10, theorem 7). See also (Behrens 13, section 1).
The -localization map is surjective on non-negative homotopy groups:
For review see also (Lorman 13). That factors through is in (Lorman 13, p. 4)
Hence: the image of is essentially the first chromatic layer of the sphere spectrum.
To say what all this means, we recall now Bousfield localization of spectra and then indicate the tower of localizations at the Morava E-theory spectra, the “chromatic filtration”.
Let be a spectrum.
Say that another spectrum is an -acyclic spectrum if the smash product is zero, .
Say that is an -local spectrum if every morphism out of an -acyclic spectrum is homotopic to the zero morphism.
Say that a morphism is an -equivalence if it becomes an equivalence after smash product with .
(e.g. Lurie, Lecture 20, example 4)
For a spectrum, every other spectrum sits in an essentially unique homotopy cofiber sequence
where is -acyclic, and is -local, def. .
Here is characterized by two properties
is -local;
is an -equivalence
(e.g. Lurie, Lecture 20, example 4)
Given , the natural morphisms in prop. exhibit the localization of an (infinity,1)-category called Bousfield localization at .
(e.g. Lurie, Lecture 20, example 5)
For an E-∞ algebra over an E-∞ ring and for an -∞-module, consider the dual Cech nerve cosimplicial object
By example each term is -local, so that the map to the totalization
factors through the -localization of
Under suitable condition the second map here is indeed an equivalence, in which case the totalization of the dual Cech nerve exhibits the -localization. This happens for instance in the discussion of the Adams spectral sequence, see the examples given there.
For a prime number, let
be the corresponding Eilenberg-MacLane spectrum. Then a spectrum which corresponds to a chain complex under the stable Dold-Kan corespondence is -local, def. , if that chain complex has chain homology groups being -modules.
The -localization of a spectrum in this case is called p-localization.
(e.g. Lurie, Lecture 20, example 8)
Let
be a perfect field of characteristic ;
be a formal group of height over .
Write for the ring of Witt vectors. Write
for the ring of formal power series over this ring, in variables; called the Lubin-Tate ring.
The Lubin-Tate formal group is the universal deformation of in that for every infinitesimal thickening of , induces a bijection
between the -algebra-homomorphisms from into and the deformations of .
(e.g. Lurie 10, lect 21, theorem 5)
By the discussion there, this is Landweber exact, hence defines a cohomology theory. Therefore by the Landweber exact functor theorem there is an even periodic cohomology theory represented by a spectrum with the property that its homotopy groups are
for of degree 2. This is called alternatively th Morava E-theory, or Lubin-Tate theory or Johnson-Wilson theory.
(e.g. Lurie, lect 22)
For each prime and for each natural number there is a Bousfield localization of spectra
where is the th Morava E-theory (for the given prime ), called the th chromatic localization. These arrange into the chromatic tower which for each spectrum is of the form
The homotopy fibers of each stage of the tower
is called the th monochromatic layer of .
Summing up the above, we need a means to compute homotopy groups of -localized spectra. In (Lurie, Higher Algebra, section 1.2.2) is given a general spectral sequence of a filtered stable homotopy type which computes homotopy groups of spectra, and in (Lurie 10, lectures 8 and 9) is discussed that the totalization of the coskeleton filtration on the dual Cech nerve of an E-∞ algebra yields the -localization. Taken together this is just what we need… and this is the general -Adams spectral sequence. We follow the nice exposition in (Wilson 13).
First we recall
for the general case of filtered objects in suitable stable (∞,1)-categories. Then we consider the specialization of that to the
In conclusion this yields for each suitable E-∞ algebra over and -∞-module a spectral sequence converging to the homotopy groups of the -localization of , and this is
We discuss the spectral sequence of a filtered stable homotopy type.
Let throughout be a stable (∞,1)-category, an abelian category, and a homological functor on , i.e., a functor that transforms every cofiber sequence
in into a long exact sequence
in . We write .
is arbitrary, is the category of abelian groups and is taking the 0th homotopy group of the mapping spectrum out of some object
is equipped with a t-structure, is the heart of the t-structure, and is the canonical functor.
is the derived category of the abelian category and is the degree-0 chain homology functor.
Any of the above with and replaced by their opposite categories.
A filtered object in an (∞,1)-category in is simply a sequential diagram
This appears as (Higher Algebra, def. 1.2.2.9).
We will take the view that the object being filtered is the homotopy limit
We could also consider the sequential diagram as a filtering of its homotopy colimit, but this is really an equivalent point of view since we can replace by .
Let be a linearly ordered set. An -chain complex in a stable (∞,1)-category is an (∞,1)-functor
such that
for each , is the zero object;
for all the induced diagram
is a homotopy pullback square.
This is Higher Algebra, def. 1.2.2.2.
Given a -chain complex in as in def. , setting
and defining a differential induced from the connecting homomorphisms of the defining homotopy fiber sequences
yields an ordinary chain complex in the homotopy category.
(Higher Algebra, remark 1.2.2.3)
Consider the inclusion of posets
given by
The induced (∞,1)-functor
restricts to an equivalence between the (∞,1)-category of -chain complexes in (def. ) and that of generalized filtered objects in (def. ).
This is Higher Algebra, lemma 1.2.2.4. The inverse functor can be described informally as follows: given a filtered object , the associated chain complex is given by
Let be a filtered object in the sense of def. . Write for the corresponding chain complex, according to prop. .
Then for all there is a long exact sequence of homotopy groups in of the form
Define then for and the object by the canonical epi-mono factorization
in the abelian category , and define the differential
to be the restriction of the connecting homomorphism
from the above long exact sequence (with , , and ).
(Higher Algebra, construction 1.2.2.6)
and there are natural (in ) isomorphisms
Thus, is a bigraded spectral sequence in the abelian category , functorial in the filtered object , with
(Higher Algebra, prop. 1.2.2.7)
If sequential limits and sequential colimits exist in , we can form the limiting term of this spectral sequence.
On the other hand, the graded object admits a filtration by
and we would like to compare with the associated graded of this filtration. We say that
The spectral sequence converges weakly if there is a canonical isomorphism
for every .
We say that the spectral sequence converges strongly if it converges weakly and if, in addition, the filtration is complete on both sides.
The meaning of the word canonical in def. is somewhat subtle since, in general, there is no map from one side to the other. However, there always exists a canonical relation between the two, and we ask that this relation be an isomorphism (see Hilton-Stammbach, VIII.7).
Let be a stable (∞,1)-category and let be a homological functor where is an abelian category which admits sequential limits. Let be a filtered object in such that exists. Suppose further that:
Then the spectral sequence in converges strongly (def. ). We write:
There is also a dual statement in which limits are replaced by colimits, but it is in fact a special case of the proposition with replaced by . A proof of this proposition (in dual form) is given in (Higher Algebra, prop. 1.2.2.14). Review is in (Wilson 13, theorem 1.2.1).
For the traditional statement in the category of chain complexes see at spectral sequence of a filtered complex.
Plenty of types of spectral sequences turn out to be special cases of this general construction.
We discuss now the special case of coskeletally filtered totalizations coming from the canonical cosimplicial objects induced from E-∞ algebras (dual Cech nerves/Sweedler corings/Amitsur complexes).
In this form this appears as (Lurie 10, theorem 2). A review is in (Wilson 13, 1.3). For the analog of this in the traditional formulation see (Ravenel, ch. 3, prop. 3.1.2).
Given an cosimplicial object in an (∞,1)-category with (∞,1)-colimits
its totalization is filtered, def. , by the totalizations of its coskeleta
The filtration spectral sequence, prop. , applied to the filtration of a totalization by coskeleta as in def. , we call the spectral sequence of a simplicial stable homotopy type.
(Higher Algebra, prop. 1.2.4.5)
The spectral sequence of a simplicial stable homotopy type has as first page/-term the cohomology groups of the Moore complex associated with the cosimplicial objects of homotopy groups
By the discussion at ∞-Dold-Kan correspondence and spectral sequence of a filtered stable homotopy type. This appears as (Higher Algebra, remark 1.2.4.4). Review is around (Wilson 13, theorem 1.2.4).
Let be an E-∞ ring and let be an E-∞ algebra over , hence an E-∞ ring equipped with a homomorphism
The canonical cosimplicial object associated to this (the -Cech nerve/Sweedler coring/Amitsur complex) is that given by the iterated smash product/tensor product over :
More generally, for an -∞-module, the canonical cosimplicial object is
If is such that the self-generalized homology (the dual -Steenrod operations) is such that as a module over it is a flat module, then there is a natural equivalence
Reviewed for instance as (Wilson 13, prop. 1.3.1).
This makes be the commutative Hopf algebroid formed by the -Steenrod algebra. See there for more on this.
The condition in prop. is satisfied for
an Eilenberg-MacLane spectrum with coefficients;
It is NOT satisfied for
.
Under good conditions (…), of the canonical cosimplicial object provides a resolution of comodule tensor product and hence computes the Ext-groups over the commutative Hopf algebroid:
(…)
There is a canonical map
from the -Bousfield localization of spectra of into the totalization.
(Lurie 10, lecture 30, prop. 1)
We consider now conditions for this morphism to be an equivalence.
Let be a connective E-∞ ring such that the core or , def. is either of
the localization of the integers at a set of primes, ;
for .
(Bousfield 79, Lurie 10, lecture 30, prop. 3, Lurie 10, lecture 31,).
Summing this up yields the general -Adams(-Novikov) spectral sequence
Let a connective E-∞ ring that satisfies the conditions of prop. . Then by prop. and prop. there is a strongly convergent multiplicative spectral sequence
converging to the homotopy groups of the -localization of . If moreover the dual -Steenrod algebra is flat as a module over , then, by prop. and remark , the -term of this spectral sequence is given by the Ext-groups over the -Steenrod Hopf algebroid.
An introduction to the chromatic perspective on the homotopy groups of spheres and the image of is in:
The bulk of the basic constructions is in
Recent surveys of the modern picture are in
and of relevance for the above discussion are particularly the following contributions there
Spectrum of the Category of Spectra_ lecture at 2013 Pre-Talbot Seminar (pdf)
image of , talk atTalbot 2013: Chromatic Homotopy Theory_ (pdf)
Loads of details for computations in the Adams spectral sequence are in
The construction of the image of the J-homomorphism when twisted by Dirichlet characters is in
Last revised on February 26, 2023 at 18:46:32. See the history of this page for a list of all contributions to it.