# Galois Extensions of Structured Ring Spectra/Stably Dualizable Groups

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The author introduces the notion of a Galois extension of commutative $S$-algebras ($E_\infty$ ring spectra), often localized with respect to a fixed homology theory. There are numerous examples, including some involving Eilenberg-Mac Lane spectra of commutative rings, real and complex topological $K$-theory, Lubin-Tate spectra and cochain $S$-algebras. He establishes the main theorem of Galois theory in this generality. Its proof involves the notions of separable and etale extensions of commutative $S$-algebras, and the Goerss-Hopkins-Miller theory for $E_\infty$ mapping spaces. He shows that the global sphere spectrum $S$ is separably closed, using Minkowski's discriminant theorem, and he estimates the separable closure of its localization with respect to each of the Morava $K$-theories. He also defines Hopf-Galois extensions of commutative $S$-algebras and studies the complex cobordism spectrum $MU$ as a common integral model for all of the local Lubin-Tate Galois extensions. The author extends the duality theory for topological groups from the classical theory for compact Lie groups, via the topological study by J. R. Klein and the $p$-complete study for $p$-compact groups by T. Bauer, to a general duality theory for stably dualizable groups in the $E$-local stable homotopy category, for any spectrum $E$.H. S. Bergsaker, K(n)-compact spheres, University of Oslo Mastera#39;s thesis, available at http://folk.uio.no/hakonsb/math/thesis.pdf (2005). A. K. Bousfield, The localization of spaces with respect to homology, Topology 14 (1975), 133a150.

 Title : Galois Extensions of Structured Ring Spectra/Stably Dualizable Groups Author : John Rognes Publisher : American Mathematical Soc. - 2008