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Spherical varieties and norm relations in Iwasawa theory

Norm-compatible families of cohomology classes for Shimura varieties, and other arithmetic symmetric spaces, play an important role in Iwasawa theory of automorphic forms. The aim of this note is to give a systematic approach to proving "vertical" norm-compatibility relations for such classes (where the level varies at a fixed prime p), treating the case of Betti and étale cohomology at once, and revealing an unexpected relation to the theory of spherical varieties. This machinery can be used to construct many new examples of norm-compatible families, potentially giving rise to new constructions of both Euler systems and p-adic L-functions: examples include families of algebraic cycles on Shimura varieties for U(n) x U(n+1) and U(2n) over the p-adic anticyclotomic tower.