Fourier algebras on homogeneous spaces

Abstract

Spectral synthesis and operator synthesis on a homogeneous space G / K , where K is a compact subgroup of a locally compact group G, are studied. Injection theorem for sets of spectral synthesis for A ( G / K ) is proved, extending the classical result of Reiter and more recent results of Kaniuth–Lau, Parthasarathy–Prakash and others. A simple direct image theorem for spectral synthesis is proved and an extension of the subgroup theorem and an alternate proof of the injection theorem are obtained as consequences. The relation between synthesis in the Fourier algebra A ( G / K ) and an appropriate Varopoulos algebra is obtained, subsuming earlier results of Varopoulos, Spronk–Turowska and Parthasarathy–Prakash. Study of relations between spectral synthesis and operator synthesis pioneered by Arveson and carried forward recently by Shulman–Turowska, Parthasarathy–Prakash and Ludwig–Turowska is undertaken on homogeneous spaces. Operator space methods are needed for this study, and more specifically, a characterisation of completely bounded multipliers on A ( G / K ) as the invariant part of a suitable weak ⁎ Haagerup tensor product (or the space of Schur multipliers) is given and is used for this study.