The cyclic and epicyclic sites

  • Alain Connes

    Institut des Hautes Études Scientifiques, Bures-Sur-Yvette, France
  • Caterina Consani

    The Johns Hopkins University, Baltimore, USA


We determine the points of the epicyclic topos which plays a key role in the geometric encoding of cyclic homology and the lambda operations. We show that the category of points of the epicyclic topos is equivalent to projective geometry in characteristic one over algebraic extensions of the infinite semifield of "max-plus integers" . An object of this category is a pair of a semimodules over an algebraic extension of . The morphisms are projective classes of semilinear maps between semimodules. The epicyclic topos sits over the arithmetic topos of [6] and the fibers of the associated geometric morphism correspond to the cyclic site. In two appendices we review the role of the cyclic and epicyclic toposes as the geometric structures supporting cyclic homology and the lambda operations.

Cite this article

Alain Connes, Caterina Consani, The cyclic and epicyclic sites. Rend. Sem. Mat. Univ. Padova 134 (2015), pp. 197–237

DOI 10.4171/RSMUP/134-5