zbMATH — the first resource for mathematics

Cohomology of classical algebraic groups from the functorial viewpoint. (English) Zbl 1208.20043
For the general linear group \(\text{GL}_n\) over a field of positive characteristic, it has been known that certain rational cohomology can be identified with certain extensions in the category of strict polynomial bifunctors. This relationship has been a key tool in recent finite generation results as well as for making explicit cohomological computations.
In this work, the author uses classical invariant theory to extend this identification to a finite product of general linear groups \(\text{GL}_n\), symplectic groups \(\text{Sp}_n\), and orthogonal groups \(\text{O}_{n,n}\) over arbitrary commutative rings (assuming that 2 is invertible in the ring if an orthogonal group is involved). Somewhat more precisely, for such a group \(G\), the author constructs a graded, natural map \(\text{Ext}^*_{\mathcal P}(\Gamma^*(F_G),F)\to H^*(G,F_n)\) that is compatible with cup products, where \(\mathcal P\) is an appropriate category of strict polynomial functors associated to \(G\), \(F_G\) is a certain “characteristic” functor in \(\mathcal P\) associated to \(G\), \(\Gamma^*\) denotes divided powers, \(F\) is an arbitrary functor in \(\mathcal P\), and \(F_n\) is a \(G\)-module obtained by an appropriate evaluation of \(F\) (determined by \(G\)). The map is then shown to be an isomorphism if the rank of \(G\) is sufficiently large relative to the degree of \(F\) (e.g., \(2n\geq\deg(F)\) in the case of \(\text{GL}_n\)).
A number of applications of this result are then given. First, it follows that the cohomology groups \(H^*(G,F_n)\) stabilize as \(n\) increases. Working over a field, the author constructs an external coproduct on these stable cohomology groups (for which the cup product is a section) and shows that with this coproduct the stable cohomology groups have the structure of a graded Hopf monoidal functor. Moreover, if the functor \(F\) admits a Hopf algebra structure, then the stable cohomology admits a Hopf algebra structure (without antipode). Following the work of A. Djament and C. Vespa [Ann. Sci. Éc. Norm. Supér. (4) 43, No. 3, 395-459 (2010; Zbl 1221.20036)] for finite classical groups, the author makes some explicit computations of the stable cohomology for orthogonal and symplectic groups with coefficients arising from symmetric and exterior power functors. One further consequence of the coproduct result is that the cup product \(H^*(G,(F_1)_n)\otimes H^*(G,(F_2)_n)\to H^*(G,(F_1)_n\otimes (F_2)_n)\) is necessarily an injection (again, for \(n\) sufficiently large relative to the degrees of the functors \(F_1\) and \(F_2\)).

20G10 Cohomology theory for linear algebraic groups
18G10 Resolutions; derived functors (category-theoretic aspects)
18A25 Functor categories, comma categories
20G35 Linear algebraic groups over adèles and other rings and schemes
14L24 Geometric invariant theory
Full Text: DOI arXiv
[1] Andersen, H.H.; Jantzen, J.C., Cohomology of induced representations for algebraic groups, Math. ann., 269, 4, 487-525, (1984) · Zbl 0529.20027
[2] Bühler, T., Exact categories, Expo. math., 28, 1-69, (2010) · Zbl 1192.18007
[3] Chałupnik, M., Extensions of strict polynomial functors, Ann. sci. école norm. sup. (4), 38, 5, 773-792, (2005) · Zbl 1089.20029
[4] Chaput, E.; Romagny, M., On the adjoint quotient of Chevalley groups over arbitrary base schemes · Zbl 1202.13004
[5] Cline, E.; Parshall, B.; Scott, L.; van der Kallen, W., Rational and generic cohomology, Invent. math., 39, 143-163, (1977) · Zbl 0336.20036
[6] de Concini, C.; Procesi, C., A characteristic free approach to invariant theory, Adv. math., 21, 3, 330-354, (1976) · Zbl 0347.20025
[7] Djament, A.; Vespa, C., Sur l’homologie des groupes orthogonaux et symplectiques à coefficients tordus, Ann. sci. école norm. sup. (4), 43, (2010) · Zbl 1221.20036
[8] Franjou, V.; Friedlander, E.M., Cohomology of bifunctors, Proc. London math. soc. (3), 97, 2, 514-544, (2008) · Zbl 1153.20042
[9] Franjou, V.; Friedlander, E.; Scorichenko, A.; Suslin, A., General linear and functor cohomology over finite fields, Ann. of math. (2), 150, 2, 663-728, (1999) · Zbl 0952.20035
[10] Friedlander, E.; Suslin, A., Cohomology of finite group schemes over a field, Invent. math., 127, 209-270, (1997) · Zbl 0945.14028
[11] Grothendieck, A., Sur quelques points d’algèbre homologique, Tôhoku math. J. (2), 9, 119-221, (1957), (in French) · Zbl 0118.26104
[12] Jantzen, J.-C., Representations of algebraic groups, Math. surveys monogr., vol. 107, (2003), Amer. Math. Soc. Providence, RI
[13] Knus, M.-A.; Merkurjev, A.; Rost, M.; Tignol, J.-P., The book of involutions, Amer. math. soc. colloq. publ., ISBN: 0-8218-0904-0, vol. 44, (1998), Amer. Math. Soc. Providence, RI, xxii+593 pp
[14] Mac Lane, S., Homology, Classics math., ISBN: 3-540-58662-8, (1995), Springer-Verlag Berlin, x+422 pp · Zbl 0818.18001
[15] Mac Lane, S., Categories for the working Mathematician, Grad. texts in math., ISBN: 0-387-98403-8, vol. 5, (1998), Springer-Verlag New York, xii+314 pp · Zbl 0906.18001
[16] Pirashvili, T., Introduction to functor homology. rational representations, the Steenrod algebra and functor homology, (), 1-26 · Zbl 1072.18009
[17] Quillen, D., Higher algebraic K-theory. I. algebraic K-theory, (), 85-147 · Zbl 0292.18004
[18] Suslin, A.; Friedlander, E.; Bendel, C., Infinitesimal 1-parameter subgroups and cohomology, J. amer. math. soc., 10, 3, 693-728, (1997) · Zbl 0960.14023
[19] Touzé, A., Universal classes for algebraic groups, Duke math. J., 151, 2, 219-249, (2010) · Zbl 1196.20052
[20] Touzé, A.; van der Kallen, W., Bifunctor cohomology and cohomological finite generation for reductive groups, Duke math. J., 151, 2, 251-278, (2010) · Zbl 1196.20053
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. It attempts to reflect the references listed in the original paper as accurately as possible without claiming the completeness or perfect precision of the matching.