Ravenel's Local-Global Conjecture for formal module Ext groups

Let K/QK/\mathbb{Q} be a finite field extension with ring of integers AA. For a prime ideal p\mathfrak{p} of AA, write ApA_{\mathfrak{p}} for the localization of AA at p\mathfrak{p}. Let LA,LABL^A,L^AB be the classifying Hopf algebroid for one-dimensional formal AA-modules and let VAp,VApTV^{A_{\mathfrak{p}}},V^{A_{\mathfrak{p}}}T be the classifying Hopf algebroid for ApA_{\mathfrak{p}}-typical one-dimensional formal modules. For every s,ts,t, every prime ideal p\mathfrak{p}, and every graded (LA,LAB)(L^A,L^AB)-comodule MM, Ravenel's Local-Global Conjecture. There exists an isomorphism of ApA_{\mathfrak{p}}-modules

ApAExt(LA,LAB)s,t(LA,M)Ext(VAp,VApT)s,t(VAp,VApLApM).A_{\mathfrak{p}} \otimes_A \operatorname{Ext}_{(L^A,L^AB)}^{s,t}(L^A,M) \cong \operatorname{Ext}_{(V^{A_{\mathfrak{p}}},V^{A_{\mathfrak{p}}}T)}^{s,t}(V^{A_{\mathfrak{p}}},V^{A_{\mathfrak{p}}}\otimes_{L^{A_{\mathfrak{p}}}}M).

This asserts compatibility between global and local computations of Ext groups for formal AA-modules. The conjecture was proven in full generality by A. Pearlman using Cartier typicalization and a Hopf algebroid change-of-rings argument.

Sources & referencesView supporting material

Primary source

A. Salch, “Ravenel's Global Conjecture is true”, arXiv:1511.05288 (2015).

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