On Completions of Hecke Algebras

  • Maarten SolleveldEmail author
Part of the Progress in Mathematics book series (PM, volume 328)


Let G be a reductive p-adic group and let \(\mathcal H (G)^{\mathfrak s}\) be a Bernstein block of the Hecke algebra of G. We consider two important topological completions of \(\mathcal H (G)^{\mathfrak s}\): a direct summand \(\mathcal S (G)^{\mathfrak s}\) of the Harish-Chandra–Schwartz algebra of G and a two-sided ideal \(C_r^* (G)^{\mathfrak s}\) of the reduced \(C^*\)-algebra of G. These are useful for the study of all tempered smooth G-representations. We suppose that \(\mathcal H (G)^{\mathfrak s}\) is Morita equivalent to an affine Hecke algebra \(\mathcal H (\mathcal R,q)\) – as is known in many cases. The latter algebra also has a Schwartz completion \(\mathcal S (\mathcal R,q)\) and a \(C^*\)-completion \(C_r^* (\mathcal R,q)\), both defined in terms of the underlying root datum \(\mathcal R\) and the parameters q. We prove that, under some mild conditions, a Morita equivalence \(\mathcal H (G)^{\mathfrak s}\sim _M \mathcal H (\mathcal R,q)\) extends to Morita equivalences \(\mathcal S (G)^{\mathfrak s}\sim _M \mathcal S (\mathcal R,q)\) and \(C_r^* (G)^{\mathfrak s}\sim _M C_r^* (\mathcal R,q)\). We also check that our conditions are fulfilled in all known cases of such Morita equivalences between Hecke algebras. This is applied to compute the topological K-theory of the reduced \(C^*\)-algebra of a classical p-adic group.

2010 Mathematics Subject Classification

20C08 22E50 22E35 



We thank the referee for suggestions and a careful reading.


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© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.IMAPP, Radboud UniversiteitNijmegenThe Netherlands

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