Hermitian K-theory for stable $\infty$-categories III: Grothendieck-Witt groups of rings

Baptiste Calmès (1) , Emanuele Dotto , Yonatan Harpaz , Fabian Hebestreit , Markus Land , Kristian Moi , Denis Nardin , Thomas Nikolaus , Wolfgang Steimle

1 LML - Laboratoire de Mathématiques de Lens

We establish a fibre sequence relating the classical Grothendieck-Witt theory of a ring $R$ to the homotopy $\mathrm{C}_2$-orbits of its K-theory and Ranicki's original (non-periodic) symmetric L-theory. We use this fibre sequence to remove the assumption that 2 is a unit in $R$ from various results about Grothendieck-Witt groups. For instance, we solve the homotopy limit problem for Dedekind rings whose fraction field is a number field, calculate the various flavours of Grothendieck-Witt groups of $\mathbb{Z}$, show that the Grothendieck-Witt groups of rings of integers in number fields are finitely generated, and that the comparison map from quadratic to symmetric Grothendieck-Witt theory of Noetherian rings of global dimension $d$ is an equivalence in degrees $\geq d+3$. As an important tool, we establish the hermitian analogue of Quillen's localisation-d\'evissage sequence for Dedekind rings and use it to solve a conjecture of Berrick-Karoubi.

Domains: Algebraic Geometry [math.AG]

Baptiste Calmès, Emanuele Dotto, Yonatan Harpaz, Fabian Hebestreit, Markus Land, et al.. Hermitian K-theory for stable $\infty$-categories III: Grothendieck-Witt groups of rings. 2020. ⟨hal-02941257⟩