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We reveal a correspondence between the homological torsion of the Bianchi groups and new geometric invariants, which are effectively computable thanks to their action on hyperbolic space. We use it to explicitly compute their integral group…

K-Theory and Homology · Mathematics 2011-09-09 Alexander D. Rahm

Let $Y$ be a cubic threefold with a non-Eckardt type involution $\tau$. Our first main result is that the $\tau$-equivariant category of the Kuznetsov component $\mathcal{K}u_{\mathbb{Z}_2}(Y)$ determines the isomorphism class of $Y$ for…

Algebraic Geometry · Mathematics 2024-10-22 Sebastian Casalaina-Martin , Xianyu Hu , Xun Lin , Shizhuo Zhang , Zheng Zhang

We study general properties of exotic crossed-product functors and characterise those which extend to functors on equivariant C*-algebra categories based on correspondences. We show that every such functor allows the construction of a…

Operator Algebras · Mathematics 2015-07-07 Alcides Buss , Siegfried Echterhoff , Rufus Willett

We prove a twisting theorem for nodal classes in permutation-equivariant quantum $K$-theory, and combine it with existing theorems of Givental to obtain a twisting result for general characteristic classes of the virtual tangent bundle.…

Algebraic Geometry · Mathematics 2021-01-27 Irit Huq-Kuruvilla

Building on work by Kasparov, we study the notion of Spanier-Whitehead K-duality for a discrete group. It is defined as duality in the KK-category between two C*-algebras which are naturally attached to the group, namely the reduced group…

K-Theory and Homology · Mathematics 2024-12-25 Shintaro Nishikawa , Valerio Proietti

Using a homological invariant together with an obstruction class in a certain Ext^2-group, we may classify objects in triangulated categories that have projective resolutions of length two. This invariant gives strong classification results…

Operator Algebras · Mathematics 2017-04-20 Rasmus Bentmann , Ralf Meyer

We propose the notion of a supercategory as an alternative approach to supermathematics. We show that this setting is rich to carry out many of the basic constructions of supermathematics. We also prove generalizations of a number of…

Quantum Algebra · Mathematics 2008-02-08 Martin Andler , Siddhartha Sahi

The relative Novikov conjecture states that the relative higher signatures of manifolds with boundary are invariant under orientation-preserving homotopy equivalences of pairs. In this paper, we study the relative Baum-Connes assembly map…

Operator Algebras · Mathematics 2023-04-07 Jintao Deng , Geng Tian , Zhizhang Xie , Guoliang Yu

We introduce two families of symmetric functions generalizing the factorial Schur $P$- and $Q$- functions due to Ivanov. We call them $K$-theoretic analogues of factorial Schur $P$- and $Q$- functions. We prove various combinatorial…

Combinatorics · Mathematics 2013-05-27 Takeshi Ikeda , Hiroshi Naruse

Let X be a space, intended as a possibly curved spacetime, and A a precosheaf of C*-algebras on X. Motivated by algebraic quantum field theory, we study the Kasparov and Theta-summable K-homology of A interpreting them in terms of the…

Operator Algebras · Mathematics 2015-03-02 Giuseppe Ruzzi , Ezio Vasselli

We survey work by the author and Ralf Meyer on equivariant KK-theory. Duality plays a key role in our approach. We organize the survey around the objective of computing a certain homotopy-invariant of a space equipped with a proper action…

K-Theory and Homology · Mathematics 2010-09-28 Heath Emerson

The aim of this paper is to describe the torus equivariant $K$-ring of even-dimensional complex quadrics by studying the graph equivariant $K$-theory of their corresponding GKM graphs. This involves providing a presentation for its graph…

Algebraic Topology · Mathematics 2025-11-06 Bidhan Paul

The paper studies the $K$-theoretic invariants of the crossed product $C^{*}$-algebras associated with an important family of homeomorphisms of the tori $\Bbb{T}^{n}$ called {\em Furstenberg transformations}. Using the Pimsner-Voiculescu…

Operator Algebras · Mathematics 2011-09-22 Kamran Reihani

The multipullback quantization of complex projective spaces lacks the naive quantum CW-complex structure because the quantization of an embedding of the $n$-skeleton into the $(n+1)$-skeleton does not exist. To overcome this difficulty, we…

K-Theory and Homology · Mathematics 2022-01-03 Francesco D'Andrea , Piotr M. Hajac , Tomasz Maszczyk , Albert Sheu , Bartosz Zielinski

This paper contains two results concerning the equivariant K-theory of toric varieties. The first is a formula for the equivariant K-groups of an arbitrary affine toric variety, generalizing the known formula for smooth ones. In fact, this…

K-Theory and Homology · Mathematics 2008-09-22 Suanne Au , Mu-wan Huang , Mark E. Walker

These notes are based on a lecture course given by the first author in the Sedano Winter School on K-theory held in Sedano, Spain, on January 22-27th of 2007. They aim at introducing K-theory of C^*-algebras, equivariant K-homology and…

K-Theory and Homology · Mathematics 2020-08-05 Paul F. Baum , Rubén J. Sánchez-García

In this paper, we study a generalization of twisted (groupoid) equivariant $\mathrm{K}$-theory in the sense of Freed-Moore for $\mathbb{Z}_2$-graded $\mathrm{C}^*$-algebras. It is defined by using Fredholm operators on Hilbert modules with…

K-Theory and Homology · Mathematics 2016-02-10 Yosuke Kubota

In this paper, we develop a quantitative K-theory for filtered C*-algebras. Particularly interesting examples of filtered C*-algebras include group C*-algebras, crossed product C*-algebras and Roe algebras. We prove a quantitative version…

Operator Algebras · Mathematics 2012-04-17 Hervé Oyono-Oyono , Guoliang Yu

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 use a recent result by Cuntz, Echterhoff and Li about the K-theory of certain reduced C*-crossed products to describe the K-theory of C*_r(S) when S is an inverse semigroup satisfying certain requirements. A result of Milan and Steinberg…

Operator Algebras · Mathematics 2013-03-18 Magnus Dahler Norling
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