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We propose a new homotopy invariant for Lie groupoids which generalizes the classical Lusternik-Schnirelmann category for topological spaces. We use a bicategorical approach to develop a notion of contraction in this context. We propose a…

Algebraic Topology · Mathematics 2009-08-25 Hellen Colman

The monoidal version of classical Morita theory is a theory of bialgebroids. To make this explicit we construct a bicategory the objects of which are the bialgebroids and in which equivalence of objects means that the corresponding module…

Quantum Algebra · Mathematics 2007-05-23 K. Szlachanyi

For a strict Lie 2-group, we develop a notion of Lie 2-algebra-valued differential forms on Lie groupoids, furnishing a differential graded-commutative Lie algebra equipped with an adjoint action of the Lie 2-group and a pullback operation…

Differential Geometry · Mathematics 2019-05-07 Konrad Waldorf

Using tools from the theory of Lie groupoids, we study the category of logarithmic flat connections on principal $G$-bundles, where $G$ is a complex reductive structure group. Flat connections on the affine line with a logarithmic…

Differential Geometry · Mathematics 2020-10-09 Francis Bischoff

The infinitesimal counterpart of a Lie groupoid is its Lie algebroid. As a vector bundle, it is given by the source vertical tangent bundle restricted to the identity bisection. Its sections can be identified with the invariant vector…

Category Theory · Mathematics 2025-11-11 Lory Aintablian , Christian Blohmann

We give a notion of equivalence for Fell bundles over groups, not necessarily saturated nor separable, and show that equivalent Fell bundles have Morita-Rieffel equivalent cross-sectional $C^*$-algebras. Our notion is originated in the…

Operator Algebras · Mathematics 2021-08-12 Fernando Abadie , Damián Ferraro

We provide three functorial extensions of the equivalence between localic etale groupoids and their quantales. The main result is a biequivalence between the bicategory of localic etale groupoids, with bi-actions as 1-cells, and a…

Category Theory · Mathematics 2015-10-21 Pedro Resende

Based on the usual Fedosov construction of star products for a symplectic manifold M we give a simple geometric construction of a bimodule deformation for the sections of a vector bundle over M starting with a symplectic connection on M and…

Quantum Algebra · Mathematics 2007-05-23 Stefan Waldmann

I categorify the definition of fibre bundle, replacing smooth manifolds with differentiable categories, Lie groups with coherent Lie 2-groups, and bundles with a suitable notion of 2-bundle. To link this with previous work, I show that…

Category Theory · Mathematics 2007-05-23 Toby Bartels

We develop the Morita theory of fusion 2-categories. In order to do so, we begin by proving that the relative tensor product of modules over a separable algebra in a fusion 2-category exists. We use this result to construct the Morita…

Category Theory · Mathematics 2023-06-06 Thibault D. Décoppet

Diffeological spaces are generalizations of smooth manifolds. In this paper, we study the homotopy theory of diffeological spaces. We begin by proving basic properties of the smooth homotopy groups that we will need later. Then we introduce…

Algebraic Topology · Mathematics 2015-05-13 J. Daniel Christensen , Enxin Wu

We define a notion of connection in a fibre bundle that is compatible with a singular foliation of the base. Fibre bundles equipped with such connections are in plentiful supply, arising naturally for any Lie groupoid-equivariant bundle,…

Differential Geometry · Mathematics 2021-04-29 Lachlan Ewen MacDonald

In this paper we define a monoid called the equivariant Brauer semigroup for a locally compact Hausdorff groupoid E whose elements consist of Morita equivalence classes of E-dynamical systems. This construction generalizes both the…

Operator Algebras · Mathematics 2012-08-30 Jonathan Henry Brown , Geoff Goehle

In this paper, we study diffeological spaces as certain kinds of discrete simplicial presheaves on the site of cartesian spaces with the coverage of good open covers. The \v{C}ech model structure on simplicial presheaves provides us with a…

Differential Geometry · Mathematics 2024-04-17 Emilio Minichiello

We apply the One-Sided Action Theorem from the first paper in this series to prove that Rieffel's Morita equivalence between the reduced crossed product by a proper saturated action and the generalized fixed-point algebra is a quotient of a…

Operator Algebras · Mathematics 2012-11-30 S. Kaliszewski , Paul S. Muhly , John Quigg , Dana P. Williams

Let G and K be groupoids. We present the notion of a (G_{\alpha},K_{\beta})-set and we prove a duality theorem in this context, which extends the duality theorem for graded algebras by groups. For A a unital G-graded algebra and X a finite…

Rings and Algebras · Mathematics 2021-11-30 Saradia Della Flora , Daiana Flôres , Andrea Morgado , Thaísa Tamusiunas

A nice differential-geometric framework for (non-abelian) higher gauge theory is provided by principal 2-bundles, i.e. categorified principal bundles. Their total spaces are Lie groupoids, local trivializations are kinds of Morita…

Differential Geometry · Mathematics 2019-05-07 Konrad Waldorf

We study (pre-)sheaves in bicategories on geometric categories: smooth manifolds, manifolds with a Lie group action and Lie groupoids. We present three main results: we describe equivariant descent, we generalize the plus construction to…

Algebraic Topology · Mathematics 2011-05-30 Thomas Nikolaus , Christoph Schweigert

We establish the deformation theory of Lie groupoid morphisms, describe the corresponding deformation cohomology of morphisms, and show the properties of the cohomology. We prove its invariance under isomorphisms of morphisms. Additionally,…

Differential Geometry · Mathematics 2023-12-21 Cristian Camilo Cárdenas

Orbifold groupoids have been recently widely used to represent both effective and ineffective orbifolds. We show that every orbifold groupoid can be faithfully represented on a continuous family of finite dimensional Hilbert spaces. As a…

Differential Geometry · Mathematics 2026-02-05 Jure Kalisnik