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We reconstruct hermitian K-theory via algebraic symplectic cobordism. In the motivic stable homotopy category SH(S) there is a unique morphism g : MSp -> BO of commutative ring T- spectra which sends the Thom class th^{MSp} to the Thom…

Algebraic Geometry · Mathematics 2018-03-13 Ivan Panin , Charles Walter

We construct a non-$\mathbb{A}^1$-invariant motivic ring spectrum $\mathrm{KO}$ over $\mathrm{Spec}(\mathbb{Z})$, whose associated cohomology theory on qcqs derived schemes is the Grothendieck-Witt theory of classical symmetric forms (as…

Algebraic Geometry · Mathematics 2025-08-13 Marc Hoyois , Markus Land

We make some computations in stable motivic homotopy theory over Spec \mathbb{C}, completed at 2. Using homotopy fixed points and the algebraic K-theory spectrum, we construct a motivic analogue of the real K-theory spectrum KO. We also…

Algebraic Topology · Mathematics 2010-02-12 Daniel C. Isaksen , Armira Shkembi

The aim of this paper is to show that Besser syntomic cohomology is representable by a rational ring spectrum in the motivic homotopical sense. In fact, extending previous constructions, we exhibit a simple representability criterion and we…

K-Theory and Homology · Mathematics 2015-09-16 Frédéric Déglise , Nicola Mazzari

Over the past century, cohomology operations have played a crucial role in homotopy theory and its applications. A powerful framework for constructing such operations is the theory of commutative algebras in spectra. In this article, we…

K-Theory and Homology · Mathematics 2026-02-04 Brian Shin

We construct well-behaved extensions of the motivic spectra representing generalized motivic cohomology and connective Balmer--Witt K-theory (among others) to mixed characteristic Dedekind schemes on which 2 is invertible. As a consequence…

K-Theory and Homology · Mathematics 2022-02-02 Tom Bachmann

We construct a motivic Eilenberg-MacLane spectrum with a highly structured multiplication over smooth schemes over Dedekind domains which represents Levine's motivic cohomology. The latter is defined via Bloch's cycle complexes. Our method…

Algebraic Geometry · Mathematics 2013-11-20 Markus Spitzweck

In the Morel-Voevodsky motivic stable homotopy category of a quasi-compact quasi-separated scheme S, several candidates exist for a motivic spectrum representing hermitian K-theory. This note shows that the cellular absolute motivic…

K-Theory and Homology · Mathematics 2025-07-16 K. Arun Kumar , Oliver Röndigs

We study commutative complex $K$-theory, a generalised cohomology theory built from spaces of ordered commuting tuples in the unitary groups. We show that the spectrum for commutative complex $K$-theory is stably equivalent to the…

Algebraic Topology · Mathematics 2018-03-16 Simon Gritschacher

We determine the A(1)-homotopy of the topological cyclic homology of the connective real K-theory spectrum ko. The answer has an associated graded that is a free F_2[v_2^4]-module of rank 52, on explicit generators in stems -1 \le * \le 30.…

Algebraic Topology · Mathematics 2026-05-26 Gabriel Angelini-Knoll , Christian Ausoni , John Rognes

Let F be a field of characteristic different than 2. We establish surjectivity of Balmer's comparison map rho^* from the tensor triangular spectrum of the homotopy category of compact motivic spectra to the homogeneous Zariski spectrum of…

Algebraic Topology · Mathematics 2018-04-18 Jeremiah Heller , Kyle Ormsby

Consider the Tate twist $\tau \in H^{0,1}(S^{0,0})$ in the mod 2 cohomology of the motivic sphere. After 2-completion, the motivic Adams spectral sequence realizes this element as a map $\tau \colon S^{0,-1} \to S^{0,0}$, with cofiber…

Algebraic Topology · Mathematics 2017-01-19 Bogdan Gheorghe

We continue the work initiated in arXiv:1206.3645, where we introduced a new stable symmetric monoidal $(\infty,1)$-category $SH_{nc}$ encoding a motivic stable homotopy theory for the noncommutative spaces of Kontsevich and obtained a…

K-Theory and Homology · Mathematics 2013-06-18 Marco Robalo

In this paper, we build on the work from our previous paper (arXiv:2002.01556) to show that periodic rational $G$-equivariant topological $K$-theory has a unique genuine-commutative ring structure for $G$ a finite abelian group. This means…

Algebraic Topology · Mathematics 2021-04-05 Anna Marie Bohmann , Christy Hazel , Jocelyne Ishak , Magdalena Kędziorek , Clover May

We establish fundamental motivic results about hermitian K-theory without assuming that 2 is invertible on the base scheme. In particular, we prove that both quadratic and symmetric Grothendieck-Witt theory satisfy Nisnevich descent, and…

K-Theory and Homology · Mathematics 2025-01-27 Baptiste Calmès , Yonatan Harpaz , Denis Nardin

The theme of this paper is to compute hermitian $K$-groups in terms of the recently developed theory of Milnor-Witt motivic cohomology. Our approach makes use of the very effective slice spectral sequence within the motivic stable homotopy…

Algebraic Geometry · Mathematics 2025-09-23 Håkon Kolderup , Oliver Röndigs , Paul Arne Østvær

We define Grothendieck-Witt spectra in the setting of Poincar\'e $\infty$-categories and show that they fit into an extension with a K- and an L-theoretic part. As consequences we deduce localisation sequences for Verdier quotients, and…

We construct commutative algebra spectra that represent the operator $K$-theory of $C^*$-algebras, which are algebras over the commutative ring spectra that represent topological $K$-theory. The spectral multiplicative structure introduces…

Operator Algebras · Mathematics 2022-03-08 R. Vasconcellos , L. C. P. A. M. Müssnich , N. J. B. Aza

Let kq denote the very effective cover of the motivic Hermitian K-theory spectrum. We analyze the ring of cooperations $\pi^\mathbb{R}_{**}(\text{kq} \otimes \text{kq})$ in the stable motivic homotopy category $\text{SH}(\mathbb{R})$,…

Algebraic Topology · Mathematics 2026-05-15 Jackson Morris

Let k be an infinite perfect field. We provide a general criterion for a spectrum in the stable homotopy category over k to be effective, i.e. to be in the localizing subcategory generated by the suspension spectra of smooth schemes. As a…

K-Theory and Homology · Mathematics 2018-07-09 Tom Bachmann , Jean Fasel
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