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In this note, we give a general method to obtain unstable motivic cell structures, following Wendt's application of the Bialynicki-Birula algebraic Morse theory. We then apply the method to spherical varieties, with special attention to the…

K-Theory and Homology · Mathematics 2018-05-14 Konrad Voelkel

We investigate several aspects of the Bialynicki-Birula decomposition of a smooth complete $\mathbb{G}_m$-variety with finite fixed locus. Our results include novel characterizations of when the Bialynicki-Birula decomposition is filterable…

Algebraic Geometry · Mathematics 2026-05-01 Teddy Gonzales , Chayim Lowen

Recently, V. Chernousov, S. Gille and A. Merkurjev have obtained a decomposition of the motive of an isotropic smooth projective homogeneous variety analogous to the Bruhat decomposition. Using the method of Bialynicki-Birula, I generalize…

Algebraic Geometry · Mathematics 2009-11-10 Patrick Brosnan

We consider a complex smooth projective variety equipped with an action of an algebraic torus with a finite number of fixed points. We compare the motivic Chern classes of Bia{\l}ynicki-Birula cells with the $K$-theoretic stable envelopes…

Algebraic Geometry · Mathematics 2021-11-08 Jakub Koncki

We introduce the notion of Q-filtrable varieties: projective varieties with a torus action and a finite number of fixed points, such that the cells of the associated Bialynicki-Birula decomposition are all rationally smooth. Our main…

Algebraic Geometry · Mathematics 2014-11-11 Richard Gonzales

We generalize the Bia{\l}ynicki-Birula decomposition from actions of $G_m$ on smooth varieties to actions of linearly reductive group ${\bf G}$ on finite type schemes and algebraic spaces. We also provide a relative version and briefly…

Algebraic Geometry · Mathematics 2018-12-24 Joachim Jelisiejew , Łukasz Sienkiewicz

We analyze stabilization with respect to ${\mathbb P}^1$ in the Morel--Voevodsky unstable motivic homotopy theory. We introduce a refined notion of cellularity (a.k.a., biconnectivity) in various motivic homotopy categories taking into…

Algebraic Geometry · Mathematics 2026-01-26 Aravind Asok , Tom Bachmann , Michael J. Hopkins

We reconstruct (appropriately completed) categories of cellular motivic spectra over fields of small cohomological dimension in terms of only their absolute Galois groups. As our main application, we determine the motivic stable stems (away…

Algebraic Geometry · Mathematics 2025-03-18 Tom Bachmann , Robert Burklund , Zhouli Xu

Let $k$ be a perfect field and $X$ be a smooth projective surface over $k$ with a rational point, we discuss the condition of splitting off the top cell for the motivic stable homotopy type of $X$. We also study some outlying examples, such…

Algebraic Geometry · Mathematics 2025-07-09 Haoyang Liu

These notes, written version of a Bourbaki talk, survey Morel-Voevodsky's motivic homotopy theory over a field, with a focus on computations of motivic homotopy sheaves, both stable and unstable. We also describe Isaksen-Wang-Xu's…

Algebraic Geometry · Mathematics 2025-10-21 Frédéric Déglise

In this paper, we discuss the motivic stable homotopy type of abelian varieties. For an abelian variety over a perfect field $k$ with a rational point, it always splits off a top-dimensional cell in motivic stable homotopy category…

Algebraic Geometry · Mathematics 2025-07-09 Haoyang Liu

In this paper, we produce a cellular motivic spectrum of motivic modular forms over $\R$ and $\C$, answering positively to a conjecture of Dan Isaksen. This spectrum is constructed to have the appropriate cohomology, as a module over the…

Algebraic Topology · Mathematics 2017-04-26 Nicolas Ricka

Using the trivial fiber topology we describe motivic $\infty$-loop spaces and fibrant replacements in the motivic stable homotopy category $\mathbf{SH}_{\mathbb{A}^1,\mathrm{Nis}}(B)$ defined over one-dimensional base schemes $B$.

Algebraic Geometry · Mathematics 2021-12-15 Andrei Druzhinin

Using Hilbert-Burch matrices, we give an explicit description of the Bia{\l}ynicki-Birula cells on the Hilbert scheme of points on $\mathbb A ^2$ with isolated fixed points. If the fixed point locus is positive dimensional we obtain an…

Algebraic Geometry · Mathematics 2026-02-12 Piotr Oszer

In this paper, we present the calculations of cellular $\mathbb{A}^1$-homology for smooth toric varieties, along with an explicit description of pure shellable cases. Consequently, we derive the (Milnor-Witt) motivic decomposition for these…

Algebraic Geometry · Mathematics 2025-05-08 Haoyang Liu , Keyao Peng

Let $X$ be a compact connected Riemann surface of genus $g \geq 2$ and $G$ a connected reductive affine algebraic group over $\mathbb{C}$. We prove the semiprojectivity of the moduli spaces of semistable $G$-Higgs bundles and $G$-bundles…

Algebraic Geometry · Mathematics 2026-03-03 Sumit Roy , Anoop Singh

We compute the 1-line of stable homotopy groups of motivic spheres over fields of characteristic not two in terms of hermitian and Milnor K-groups. This is achieved by solving questions about convergence and differentials in the slice…

Algebraic Topology · Mathematics 2018-08-15 Oliver Röndigs , Markus Spitzweck , Paul Arne Østvær

In this paper, we continue the program initiated by Kahn-Saito-Yamazaki by constructing and studying an unstable motivic homotopy category with modulus, extending the Morel-Voevodsky construction from smooth schemes over a field $k$ to…

Algebraic Geometry · Mathematics 2019-10-04 Federico Binda

We study the motivic Grothendieck group of algebraic varieties from the point of view of stable birational geometry. In particular, we obtain a counter-example to a conjecture of M. Kapranov on the rationality of motivic zeta-function.

Algebraic Geometry · Mathematics 2007-05-23 Michael Larsen , Valery A. Lunts

We compute the 2-line of stable homotopy groups of motivic spheres over fields of characteristic not two in terms of motivic cohomology and hermitian K-groups.

Algebraic Geometry · Mathematics 2021-04-01 Oliver Röndigs , Markus Spitzweck , Paul Arne Østvær
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