Hostname: page-component-8448b6f56d-jr42d Total loading time: 0 Render date: 2024-04-25T04:41:37.170Z Has data issue: false hasContentIssue false

GLOBAL ACTIONS AND VECTOR $K$-THEORY

Published online by Cambridge University Press:  15 January 2020

ANTHONY BAK
Affiliation:
Fakulät für Mathematik, Universität Bielefeld, Bielefeld - 33501, Germany; bak.biel@googlemail.com
ANURADHA S. GARGE
Affiliation:
Department of Mathematics, University of Mumbai, Mumbai - 400098, India; anuradha.garge@gmail.com

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Purely algebraic objects like abstract groups, coset spaces, and G-modules do not have a notion of hole as do analytical and topological objects. However, equipping an algebraic object with a global action reveals holes in it and thanks to the homotopy theory of global actions, the holes can be described and quantified much as they are in the homotopy theory of topological spaces. Part I of this article, due to the first author, starts by recalling the notion of a global action and describes in detail the global actions attached to the general linear, elementary, and Steinberg groups. With these examples in mind, we describe the elementary homotopy theory of arbitrary global actions, construct their homotopy groups, and revisit their covering theory. We then equip the set $Um_{n}(R)$ of all unimodular row vectors of length $n$ over a ring $R$ with a global action. Its homotopy groups $\unicode[STIX]{x1D70B}_{i}(Um_{n}(R)),i\geqslant 0$ are christened the vector $K$-theory groups $K_{i+1}(Um_{n}(R)),i\geqslant 0$ of $Um_{n}(R)$. It is known that the homotopy groups $\unicode[STIX]{x1D70B}_{i}(\text{GL}_{n}(R))$ of the general linear group $\text{GL}_{n}(R)$ viewed as a global action are the Volodin $K$-theory groups $K_{i+1,n}(R)$. The main result of Part I is an algebraic construction of the simply connected covering map $\mathit{StUm}_{n}(R)\rightarrow \mathit{EUm}_{n}(R)$ where $\mathit{EUm}_{n}(R)$ is the path connected component of the vector $(1,0,\ldots ,0)\in Um_{n}(R)$. The result constructs the map as a specific quotient of the simply connected covering map $St_{n}(R)\rightarrow E_{n}(R)$ of the elementary global action $E_{n}(R)$ by the Steinberg global action $St_{n}(R)$. As expected, $K_{2}(Um_{n}(R))$ is identified with $\text{Ker}(\mathit{StUm}_{n}(R)\rightarrow \mathit{EUm}_{n}(R))$. Part II of the paper provides an exact sequence relating stability for the Volodin $K$-theory groups $K_{1,n}(R)$ and $K_{2,n}(R)$ to vector $K$-theory groups.

Type
Algebra
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s) 2020

References

Bak, A., ‘Global actions: the algebraic counterpart of a topological space’, Uspeki Mat. Nauk., English translation: Russian Math. Surveys 525 (1997), 955996.Google Scholar
Bak, A., Brown, R., Minian, G. and Porter, T., ‘Global actions, groupoid atlases and applications’, J. Homotopy Relat. Struct. 1(1) (2006), 101167 (electronic).Google Scholar
Bass, H., ‘K-theory and stable algebra’, Publ. Math. Inst. Hautes Études Sci. 22 (1964), 489544.CrossRefGoogle Scholar
Bass, H., Algebraic K-Theory, (W. A. Benjamin, Inc., New York–Amsterdam, 1968).Google Scholar
Bass, H., Milnor, J. and Serre, J.-P., ‘Solution of the congruence subgroup problem for SLn, (n⩾3) and Sp2n, (n⩾2)’, Publ. Math. Inst. Hautes Études Sci. 33 (1967), 59137.CrossRefGoogle Scholar
Milnor, J., Introduction to Algebraic K-Theory, Annals of Mathematics Studies, 72 (Princeton University Press, Princeton, NJ, 1971).Google Scholar
Rao, R. A. and van der Kallen, W., ‘Improved stability for $SK_{1}$ and $WMS_{d}$ of a non-singular affine algebra’. $K$-theory (Strasbourg, 1992), Astérisque 11(226) (1994), 411–420.Google Scholar
Suslin, A. A. and Tulenbayev, M. S., ‘A theorem on stabilization for Milnor’s K 2 functor. Rings and modules’, Zap. Nauchn. Sem. Leningrad. Otdel. Mat. Inst. Steklov. (LOMI) 64 (1976), 131152 (Russian).Google Scholar
Vaserstein, L. N., ‘On the stabilization of the general linear group over a ring’, Mat. Sb. (N.S.) 79(121)(3(7)) (1969), 405424.Google Scholar
van der Kallen, W., ‘A module structure on certain orbit sets of unimodular rows’, J. Pure Appl. Algebra 57 (1975), 657663.Google Scholar
van der Kallen, W., ‘A group structure on certain orbit sets of unimodular rows’, J. Algebra 82(2) (1983), 363397.CrossRefGoogle Scholar