Abstract
Let M be a topological monoid with homotopy group completion ΩBM. Under a strong homotopy commutativity hypothesis on M, we show that πk(ΩBM) is the quotient of the monoid of free homotopy classes [Sk, M] by its submonoid of nullhomotopic maps.
We give two applications. First, this result gives a concrete description of the Lawson homology of a complex projective variety in terms of pointwise addition of spherical families of effective algebraic cycles. Second, we apply this result to monoids built from the unitary, or general linear, representation spaces of discrete groups, leading to results about lifting continuous families of characters to continuous families of representations.
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References
T. Baird and D. A. Ramras, Smooth approximation in algebraic sets and the topological Atiyah–Segal map, preprint, https://arxiv.org/abs/1206.3341v3.
M. Bergeron, The topology of nilpotent representations in reductive groups and their maximal compact subgroups, Geometry and Topology 19 (2015), 1383–1407.
I. Dolgachev, Lectures on Invariant Theory, London Mathematical Society Lecture Note Series, Vol. 296, Cambridge University Press, Cambridge, 2003.
B. I. Dundas, T. G. Goodwillie and R. McCarthy, The Local Structure of Algebraic K-Theory, Algebra and Applications, Vol. 18, Springer, London, 2013.
J. Ebert and O. Randal-Williams, Semi-simplicial spaces, Algebraic & Geometric Topology, to appear, https://arxiv.org/abs/1705.03774.
B. Eckmann and P. J. Hilton, Group-like structures in general categories. I. Multiplications and comultiplications, Mathematische Annalen 145 (1961/1962), 227–255.
A. D. Elmendorf, I. Kriz, M. A. Mandell and J. P. May, Rings, Modules, and Algebras in Stable Homotopy Theory, Mathematical Surveys and Monographs, Vol. 47, American Mathematical Society, Providence, RI, 1997.
C. Florentino and S. Lawton, The topology of moduli spaces of free group representations, Mathematische Annalen 345 (2009), 453–489.
C. Florentino and S. Lawton, Topology of character varieties of Abelian groups, Topology and its Applications 173 (2014), 32–58.
C. Florentino, S. Lawton and D. Ramras, Homotopy groups of free group character varieties, Annali della Scuola Normale Superiore di Pisa. Classe di Scienze. Serie V 17 (2017), 143–185.
E. M. Friedlander, Algebraic cycles, Chow varieties, and Lawson homology, Compositio Mathematica 77 (1991), 55–93.
A. Hatcher, Algebraic Topology, Cambridge University Press, Cambridge, 2002.
H. Hironaka, Triangulations of algebraic sets, in Algebraic Geometry—Arcata 1974, Proceedings of Symposia in Pure Mathematics, Vol. 29, American Mathematical Society, Providence, RI, 1975, pp. 165–185.
H. B. Lawson, Jr., The topological structure of the space of algebraic varieties, Bulletin of the American Mathematical Society 17 (1987), 326–330.
T. Lawson, Derived representation theory of nilpotent groups, Ph.D. Thesis, Stanford University, ProQuest LLC, and Arbor, MI, 2004.
T. Lawson, The product formula in unitary deformation K-theory, K-Theory 37 (2006), 395–422.
T. Lawson, The Bott cofiber sequence in deformation K-theory and simultaneous similarity in U(n), Mathematical Proceedings of the Cambridge Philosophical Society 146 (2009), 379–393.
L. Gaunc. Lewis, Jr., The stable category and generalized Thom spectra, Ph.D. Thesis, University of Chicago, 1978.
P. Lima-Filho, Topological properties of the algebraic cycles functor, in Transcendental Aspects of Algebraic Cycles, London Mathematical Society Lecture Note Series, Vol. 313, Cambridge University Press, Cambridge, 2004, pp. 75–19.
A. Lubotzky and A. R. Magid, Varieties of representations of finitely generated groups Memoirs of the American Mathematical Society 58 (1985).
D. McDuff and G. Segal, Homology fibrations and the “group-completion” theorem, Inventiones Mathematicae 31 (1975/1976), 279–284.
J. Miller and M. Palmer, A twisted homology fibration criterion and the twisted groupcompletion theorem, Quarterly Journal of Mathematics 66 (2015), 265–284.
J. Milnor, The geometric realization of a semi-simplicial complex, Annals of Mathematics 65 (1957), 357–362.
C. Peters and S. Kosarew, Introduction to Lawson homology, in Transcendental Aspects of Algebraic Cycles, London Mathematical Society Lecture Note Series, Vol. 313, Cambridge University Press, Cambridge, 2004, pp. 44–71.
D. Ramras, R. Willett and G. Yu, A finite-dimensional approach to the strong Novikov conjecture, Algebraic & Geometric Topology 13 (2013), 2283–2316.
D. A. Ramras, Excision for deformation K-theory of free products, Algebraic & Geometric Topology 7 (2007), 2239–2270.
D. A. Ramras, The stable moduli space of flat connections over a surface, Transactions of the American Mathematical Society 363 (2011), 1061–1100.
D. A. Ramras, Periodicity in the stable representation theory of crystallographic groups, Forum Mathematicum 26 (2014), 177–219.
D. A. Ramras, The topological Atiyah–Segal map, preprint, https://arxiv.org/abs/1607.06430.
O. Randal-Williams, ‘Group-completion’, local coefficient systems and perfection, Quarterly Journal of Mathematics 64 (2013), 795–803.
G. Segal, Categories and cohomology theories, Topology 13 (1974), 293–312.
Y.-S. Wang, Geometric realization and its variants, preprint, https://arxiv.org/abs/1804.00345.
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The author was partially supported by the Simons Foundation (#279007).
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Ramras, D.A. The homotopy groups of a homotopy group completion. Isr. J. Math. 234, 81–124 (2019). https://doi.org/10.1007/s11856-019-1914-2
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DOI: https://doi.org/10.1007/s11856-019-1914-2