In this work we study the failure of the HKR theorem over rings of positive and
mixed characteristic. For this we construct a
filtered circle interpolating between the
usual topological circle and a formal version of it. By mapping to schemes we produce
this way an interpolation, realized in practice by the existence of a natural filtration,
from Hochschild and (a filtered version of) cyclic homology to derived de Rham
cohomology. In particular, we show that this recovers the filtration of Antieau
(Ann. –Theory
4 (2019) 505–519) and Bhatt, Morrow and Scholze (Publ. Math. Inst. Hautes
Études Sci. 129 (2019) 199–310). The construction of our filtered circle is based on
the theory of affine stacks and affinization introduced by the third author, together
with some facts about schemes of Witt vectors.
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