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arXiv · 2011.07241

Eisenstein cocycles in motivic cohomology

Romyar Sharifi·Akshay Venkatesh
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Abstract

Several authors have studied homomorphisms from first homology groups of modular curves to the second K-group of a cyclotomic ring or a modular curve X. These maps send Manin symbols in the homology groups to Steinberg symbols of cyclotomic or Siegel units. We give a new construction of these maps and a direct proof of their Hecke equivariance, analogous to the construction of Siegel units using the universal elliptic curve. Our main tool is a 1-cocycle from GL_2(Z) to the second K-group of the function field of a suitable group scheme over X, from which the maps of interest arise by specialization.

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Romyar Sharifi, Akshay Venkatesh. 2020-11-14. Eisenstein cocycles in motivic cohomology. https://doi.org/10.1112/s0010437x24007322

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