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We define an unstable equivariant motivic homotopy category for an algebraic group over a Noetherian base scheme. We show that equivariant algebraic $K$-theory is representable in the resulting homotopy category. Additionally, we establish…

Algebraic Topology · Mathematics 2015-10-19 Jeremiah Heller , Amalendu Krishna , Paul Arne Ostvaer

In this paper, we develop the theory of equivariant motivic homotopy theory, both unstable and stable. While our original interest was in the case of profinite group actions on smooth schemes, we discuss our results in as broad a setting as…

Algebraic Topology · Mathematics 2014-04-08 Gunnar Carlsson , Roy Joshua

The motivic homotopy categories can be defined with respect to different topologies and different underlying categories of schemes. For a number of reasons (mainly because of the Gluing Theorem) the motivic homotopy category built out of…

Algebraic Geometry · Mathematics 2008-05-30 Vladimir Voevodsky

We introduce a Bredon motivic cohomology theory for smooth schemes defined over a field and equipped with an action by a finite group. These cohomology groups are defined for finite dimensional representations as the hypercohomology of…

Algebraic Geometry · Mathematics 2014-08-12 Jeremiah Heller , Mircea Voineagu , Paul Arne Ostvaer

In this paper we study a model structure on a category of schemes with a group action and the resulting unstable and stable equivariant motivic homotopy theories. The new model structure introduced here samples a comparison to the one by…

Algebraic Topology · Mathematics 2013-12-03 Philip Herrmann

We construct a motivic spectral sequence for the relative homotopy invariant K-theory of a closed immersion of schemes $D \subset X$. The $E_2$-terms of this spectral sequence are the cdh-hypercohomology of a complex of equi-dimensional…

Algebraic Geometry · Mathematics 2019-03-13 Amalendu Krishna , Pablo Pelaez

The aim of this paper is to connect two important and apparently unrelated theories: motivic homotopy theory and ramification theory. We construct motivic homotopy categories over a qcqs base scheme $S$, in which cohomology theories with…

Algebraic Geometry · Mathematics 2025-04-04 Junnosuke Koizumi , Hiroyasu Miyazaki , Shuji Saito

For a linear algebraic group $G$ over a field $k$, we define an equivariant version of the Voevodsky's motivic cobordism $MGL$. We show that this is an oriented cohomology theory with localization sequence on the category of smooth…

Algebraic Geometry · Mathematics 2012-06-27 Amalendu Krishna

We develop a theory of motivic spectra in a broad generality; in particular $\mathbb{A}^1$-homotopy invariance is not assumed. As an application, we prove that $K$-theory of schemes is a universal Zariski sheaf of spectra which is equipped…

Algebraic Geometry · Mathematics 2025-04-18 Toni Annala , Ryomei Iwasa

We introduce and study the homotopy theory of motivic spaces and spectra parametrized by quotient stacks [X/G], where G is a linearly reductive linear algebraic group. We extend to this equivariant setting the main foundational results of…

Algebraic Geometry · Mathematics 2024-10-23 Marc Hoyois

We prove some fundamental results like localization, excision, Nisnevich descent and the Mayer-Vietoris property for equivariant regular blow-up for the equivariant K-theory of schemes with an affine group scheme action. We also show that…

Algebraic Geometry · Mathematics 2017-08-03 Amalendu Krishna , Charanya Ravi

We construct geometric models for classifying spaces of linear algebraic groups in G-equivariant motivic homotopy theory, where G is a tame group scheme. As a consequence, we show that the equivariant motivic spectrum representing the…

K-Theory and Homology · Mathematics 2020-09-16 Marc Hoyois

We use the construction of the stable homotopy category by Khan-Ravi to calculate the integral $T$-equivariant $K$-theory spectrum of a flag variety over an affine scheme, where $T$ is a split torus associated to the flag variety. More…

Algebraic Geometry · Mathematics 2025-08-20 Can Yaylali

Given a finite group G, we develop a theory of G-equivariant noncommutative motives. This theory provides a well-adapted framework for the study of G-schemes, Picard groups of schemes, G-algebras, 2-cocycles, equivariant algebraic K-theory,…

Algebraic Geometry · Mathematics 2016-08-24 Goncalo Tabuada

Let $G$ be an affine group scheme over a noetherian commutative ring $R$. We show that every $G$-equivariant vector bundle on an affine toric scheme over $R$ with $G$-action is extended from $\Spec(R)$ for several cases of $R$ and $G$. We…

Algebraic Geometry · Mathematics 2017-01-04 Amalendu Krishna , Charanya Ravi

We discuss algebraic vector bundles on smooth k-schemes X contractible from the standpoint of A^1-homotopy theory; when k = C, the smooth manifolds X(C) are contractible as topological spaces. The integral algebraic K-theory and integral…

Algebraic Geometry · Mathematics 2007-10-22 Aravind Asok , Brent Doran

We construct models for the motivic homotopy category based on simplicial functors from smooth schemes over a field to simplicial sets. These spaces are homotopy invariant and therefore one does not have to invert the affine line in order…

Algebraic Geometry · Mathematics 2010-07-20 Philip Herrmann , Florian Strunk

We study the structure of the rational motivic stable homotopy category over general base schemes. Our first class of results concerns the six operations: we prove absolute purity, stability of constructible objects, and…

Algebraic Geometry · Mathematics 2021-03-15 Frédéric Déglise , Jean Fasel , Adeel A. Khan , Fangzhou Jin

We construct an algebraic-cycle based model for the motivic cohomology on the category of schemes of finite type over a field, where schemes may admit arbitrary singularities and may be non-reduced. We show that our theory is functorial on…

Algebraic Geometry · Mathematics 2021-12-30 Jinhyun Park

This paper sets out basic properties of motivic twisted K-theory with respect to degree three motivic cohomology classes of weight one. Motivic twisted K-theory is defined in terms of such motivic cohomology classes by taking pullbacks…

Algebraic Topology · Mathematics 2010-08-31 Markus Spitzweck , Paul Arne Østvær
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