Paths and cylinders
Stable Homotopy theory
Quite generally, the term Mackey functor refers to an additive functor from a (subcategory of) a category of correspondences (in a disjunctive category ) to possibly any other additive category which however usually is the “base” abelian category. More generally the term now refers to the fairly obvious homotopy theoretic or higher categorical refinements of this concept.
Therefore the concept of Mackey functors is similar to that of sheaves with transfer and as such appears (implicitly) in the discussion of motives (explicitly e.g. in Kahn-Yamazaki 11, section 2, where is a category of suitable schemes).
The concept was however introduced and named as such in the context of representation theory (Dress 71) and equivariant homotopy theory/equivariant cohomology (May 96). Here the equivariant homotopy groups of a (genuine) G-spectrum organize into a Mackey functor on -orbits, and this plays a key role in the equivariant Whitehead theorem. In this context of equivariant stable homotopy theory Mackey functors were given a full (∞,1)-category-theoretic formulation in (Barwick 14).
We follow the modern account in (Barwick 14).
Let be a disjunctive (∞,1)-category and write for the (∞,1)-category of correspondences in , regarded as a symmetric monoidal (∞,1)-category with respect to its coproduct (which is a biproduct by disjunctiveness of ).
Write Spectra for the (∞,1)-category of spectra regarded as a symmetric monoidal (∞,1)-category with respect to direct sum. More generally could be any symmetric monoidal stable (∞,1)-category
Then a (spectral) Mackey functor on is a monoidal (∞,1)-functor of the form
Notice that this means that is in particular
a covariant (∞,1)-functor ;
a contravariant (∞,1)-functor, hence ;
satisfying the Beck-Chevalley condition.
(More generally one may specify suitably chosen sub--categories and restrict to correspondences whose left leg is in and whose right leg is in (Barwick 14, section 5).)
Dress’ Mackey functors
For taken to be (the derived category) of an abelian category (or better: postcomposed with a homological functor ) this definition reduces (Barwick 14) to that of Mackey functors as originally defined in (Dress 71).
Let be a finite group. Let be its category of permutation representations. Then is essentially what is called the Burnside category of (possibly after abelianizing/stabilizing the hom-spaces suitably, but as (Barwick 14) highlights, this is unnecessary when one is mapping out of this into something abelian/stable, as is the case here).
For finite then Mackey functors on are equivalent to genuine G-spectra (Guillou-May 11, theorem 0.1, Barwick 14, below example B.6) (Notice that this equivalence does not in general hold if is not a finite group.)
For a genuine G-spectrum then the corresponding spectral Mackey functor is given by the equivariant homotopy groups of
where on the right we have the -equivariant mapping spectrum from the (equivariant) suspension spectrum of the orbit to .
(e.g. (Guillou-May 11, remark 2.5), see also (Schwede 15, p. 16) for restriction and section 4 culminating on p. 37 for transfer and compatibility).
Further, the corresponding abelian-group valued Mackey functor is
where now on the right we have just the homotopy classes of maps, i.e. the morphisms in the equivariant stable homotopy category (e.g. Greenlees-May 95, p. 43)
Cohomology with coefficients in a Mackey functor
We discuss cohomology of topological G-spaces with coefficients in a Mackey functor, following notation and conventions as in (May 96, sections IX, X). See also (Greenlees-May 95, p. 9).
For a pointed G-CW complex, define the chain complex of Mackey functors to be given by the stable equivariant homotopy groups of the quotient spaces :
Then for any Mackey functor, the ordinary cohomology of with coefficients in is the cochain cohomology of the complex of homs of Mackey functors :
More generally, for a G-representation, the -RO(G)-graded cohomology of with coefficients in is
(May 96, section X.4 def. 4.1, def. 4.2)
The original article is
- A. W. M. Dress, Notes on the theory of representations of finite groups. Part I: The Burnside ring of a finite group and some AGN-applications, Bielefeld, 1971,
Reviews and surveys include
John Greenlees, Peter May, Equivariant stable homotopy theory, in I.M. James (ed.), Handbook of Algebraic Topology , pp. 279-325. 1995. (pdf)
Peter May, section IX.4 of Equivariant homotopy and cohomology theory CBMS Regional Conference Series in Mathematics, vol. 91, Published for the Conference Board of the Mathematical Sciences, Washington, DC, 1996. With contributions by M. Cole, G. Comeza˜na, S. Costenoble, A. D. Elmenddorf, J. P. C. Greenlees, L. G. Lewis, Jr., R. J. Piacenza, G. Triantafillou, and S. Waner. (pdf)
Peter Webb, A Guide to Mackey Functors (pdf)
Michael Hill, Michael Hopkins, Douglas Ravenel, section 4 of The Arf-Kervaire problem in algebraic topology: Sketch of the proof (pdf)
(with an eye towards application to the Arf-Kervaire invariant problem)
Megan Shulman, chapter 2 of Equivariant local coefficients and the -graded cohomology of classifying spaces (arXiv:1405.1770)
Tammo tom Dieck, Transformation groups, Studies in Mathematics, vol. 8, Walter de Gruyter, Berlin, New York, 1987, x + 311 pp.,
Serge Bouc, chapter 1 of Green Functors and G-sets, LNM 1671 (1997; paperback 2008) doi:10.1007/BFb0095821
Tammo tom Dieck, Equivariant homology and Mackey functors, Mathematische Annalen 206, no.1, pp. 67–78, 1973 doi:10.1007/BF01431529
John Greenlees, Peter May, appendix A of Generalized Tate cohomology, Mem. Amer. Math. Soc. 113 (1995) no 543 (pdf)
D. Tambara, The Drinfeld center of the category of Mackey functors, J. Algebra 319, 10, pp. 4018-4101 (2008) doi:10.1016/j.jalgebra.2008.02.011
Elango Panchadcharam, Categories of Mackey Functors, PhD thesis, Macquarie Univ. 2006
William Kronholm, The -graded Serre spectral sequence, Homology Homotopy Appl. Volume 12, Number 1 (2010), 75-92. (pdf, Euclid)
The construction of equivariant stable homotopy theory in terms of Mackey functors is due to
Lectures notes include
Application of Mackey functors to the theory of motives includes
- Bruno Kahn, Takao Yamazaki, Voevodsky’s motives and Weil reciprocity, Duke Mathematical Journal 162, 14 (2013) 2751-2796 (arXiv:1108.2764)