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We argue that various braid group actions on triangulated categories should be extended to projective actions of the category of braid cobordisms and illustrate how this works in examples. We also construct actions of both the affine braid…

Quantum Algebra · Mathematics 2007-07-29 Mikhail Khovanov , Richard Thomas

Let X be a complex, rationally connected, projective manifold. We show that X admits a modification X' that contains a quasi-line, ie a smooth rational curve whose normal bundle is a direct sum of copies of O_{P^1}(1). For manifolds…

Algebraic Geometry · Mathematics 2007-05-23 Paltin Ionescu , Daniel Naie

We prove a general form of the statement that the cohomology of a quotient stack can be computed by the Borel construction. It also applies to the lisse extensions of generalized cohomology theories like motivic cohomology and algebraic…

Algebraic Geometry · Mathematics 2025-09-29 Adeel A. Khan , Charanya Ravi

We obtain refined generating series formulae for equivariant characteristic classes of external and symmetric products of singular complex quasi-projective varieties. More concretely, we study equivariant versions of Todd, Chern and…

Algebraic Geometry · Mathematics 2018-03-16 Laurentiu Maxim , Joerg Schuermann

We prove the following classification theorem of the ``Glimm -- Effros'' type for Borel order relations: a Borel partial order on the reals either is Borel linearizable or includes a copy of a certain Borel partial order $\meo$ which is not…

Logic · Mathematics 2018-08-22 Vladimir Kanovei

The feasibility of a classification-by-rank program for modular categories follows from the Rank-Finiteness Theorem. We develop arithmetic, representation theoretic and algebraic methods for classifying modular categories by rank. As an…

Quantum Algebra · Mathematics 2016-03-23 Paul Bruillard , Siu-Hung Ng , Eric C. Rowell , Zhenghan Wang

We extend the logical categories framework to first order modal logic. In our modal categories, modal operators are applied directly to subobjects and interact with the background factorization system. We prove a Joyal-style representation…

Logic in Computer Science · Computer Science 2025-04-07 Silvio Ghilardi , Jérémie Marquès

The equivariant cohomology of a space with a group action is not only a ring but also an algebra over the cohomology ring of the classifying space of the acting group. We prove that toric manifolds (i.e. compact smooth toric varieties) are…

Algebraic Topology · Mathematics 2008-11-28 Mikiya Masuda

Bivariant theory is a unified framework for cohomology and Borel-Moore homology theories. In this paper, we extract an $\infty$-enhanced bivariant homology theory from Gaitsgory-Rozenblyum's six functor formalism.

Category Theory · Mathematics 2022-01-24 Tomoyuki Abe

We discuss two simple but useful observations that allow the construction of modular forms from given ones using invariant theory. The first one deals with elliptic modular forms and their derivatives, and generalizes the Rankin-Cohen…

Number Theory · Mathematics 2023-04-10 Fabien Cléry , Gerard van der Geer

We introduce new invariants in equivariant birational geometry and study their relation to modular symbols and cohomology of arithmetic groups.

Algebraic Geometry · Mathematics 2019-08-23 Maxim Kontsevich , Vasily Pestun , Yuri Tschinkel

Conformal transformations are obtained by demanding that the form of the metric change by a conformal factor. Nevertheless, this transformation of the metric is not taken into account when a variation of the action is performed. The basic…

High Energy Physics - Theory · Physics 2007-05-23 L. C. T. Guillen

In this paper, we prove the dg affinity of formal deformation algebroid stacks over complex smooth algebraic varieties. For that purpose, we introduce the triangulated category of formal deformation modules which are cohomologically…

Algebraic Geometry · Mathematics 2011-03-08 Francois Petit

Let X be a T-variety, where T is an algebraic torus. We describe a fully faithful functor from the category of T-equivariant vector bundles on X to a certain category of filtered vector bundles on a suitable quotient of X by T. We show that…

Algebraic Geometry · Mathematics 2019-11-26 Nathan Ilten , Hendrik Süß

We apply the equivariant Burnside group formalism to distinguish linear actions of finite groups, up to equivariant birationality. Our approach is based on De Concini-Procesi models of subspace arrangements.

Algebraic Geometry · Mathematics 2021-08-03 Andrew Kresch , Yuri Tschinkel

The rational Borel equivariant cohomology for actions of a compact connected Lie group is determined by restriction of the action to a maximal torus. We show that a similar reduction holds for any compact Lie group $G$ when there is a…

Algebraic Topology · Mathematics 2024-02-14 Sergio Chaves

For coalgebras $C$ and $D$, Takeuchi proved that the category of linear functors from $\mathfrak{M}^C$ to $\mathfrak{M}^D$ preserving small coproducts is equivalent to the category of $C$-$D$-bicomodules, where $\mathfrak{M}^C$ for a…

Quantum Algebra · Mathematics 2025-10-10 Taiki Shibata , Kenichi Shimizu

In this article, we investigate the category $\mathcal{A}^G$ of equivariant objects of an additive category $\mathcal{A}$ with respect to an action of a finite group $G$. We show that if $G$ is solvable then we can reconstruct $\mathcal{A}$…

Category Theory · Mathematics 2021-09-03 Chao Sun

We introduce partial differential encodings of Boolean functions as a way of measuring the complexity of Boolean functions. These encodings enable us to derive from group actions non-trivial bounds on the Chow-Rank of polynomials used to…

Computational Complexity · Computer Science 2022-12-02 Edinah K. Gnang , Rongyu Xu

Let $X$ be a 3-dimensional affine variety with a faithful action of a 2-dimensional torus $T$. Then the space of first order infinitesimal deformations $T^1(X)$ is graded by the characters of $T$, and the zeroth graded component $T^1(X)_0$…

Algebraic Geometry · Mathematics 2015-09-08 Rostislav Devyatov