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We establish cartesian model structures for variants of $\Theta_n$-spaces in which we replace some or all of the completeness conditions by discreteness conditions. We prove that they are all equivalent to each other and to the…

Algebraic Topology · Mathematics 2025-01-30 Julia E. Bergner

We consider the derived category of coherent sheaves on a complex vector space equivariant with respect to an action of a finite reflection group G. In some cases, including Weyl groups of type A, B, G_2, F_4, as well as the groups…

Algebraic Geometry · Mathematics 2017-06-07 Alexander Polishchuk , Michel Van den Bergh

To a smooth and proper morphism $\mathcal{X}\to U$ with quasicompact semiseparated target we associate a sheaf in the \'etale topology, which takes an affine $U$-scheme $V$ to the set of $V$-linear semiorthogonal decompositions (of fixed…

Algebraic Geometry · Mathematics 2025-11-17 Pieter Belmans , Shinnosuke Okawa , Andrea T. Ricolfi

In the preceding paper, we have constructed a compactly generated model structure on the category $\dcal$ of diffeological spaces together with the adjoint pairs $|\ |_\dcal : \scal \rightleftarrows \dcal : S^\dcal$ and $\tilde{\cdot} :…

Algebraic Topology · Mathematics 2017-02-15 Hiroshi Kihara

In this paper, we address the construction of homotopy bicategories of $(\infty,2)$-categories, which we take as being modeled by 2-fold Segal spaces. Our main result is the concrete construction of a functor $h_2$ from the category of…

Category Theory · Mathematics 2025-02-14 Jack Romö

A 10-dimensional symplectic moduli space of torsion sheaves on the cubic 4-fold is constructed. It parametrizes the stable rank 2 vector bundles on the hypeplane sections of the cubic 4-fold which are obtained by Serre's construction from…

Algebraic Geometry · Mathematics 2007-05-23 D. Markushevich , A. S. Tikhomirov

In this note we consider partial model categories, by which we mean relative categories that satisfy a weakened version of the model category axioms involving only the weak equivalences. More precisely, a partial model category will be a…

Algebraic Topology · Mathematics 2013-01-22 C. Barwick , D. M. Kan

This is an exposition of homotopical results on the geometric realization of semi-simplicial spaces. We then use these to derive basic foundational results about classifying spaces of topological categories, possibly without units. The…

Algebraic Topology · Mathematics 2019-08-21 Johannes Ebert , Oscar Randal-Williams

We use basic tools of descriptive set theory to prove that a closed set $\mathcal S$ of marked groups has $2^{\aleph_0}$ quasi-isometry classes provided every non-empty open subset of $\mathcal S$ contains at least two non-quasi-isometric…

Group Theory · Mathematics 2022-07-08 Ashot Minasyan , Denis Osin , Stefan Witzel

In this paper we complete a chain of explicit Quillen equivalences between the model category for $\Theta_{n+1}$-spaces and the model category of small categories enriched in $\Theta_n$-spaces. The Quillen equivalences given here connect…

Algebraic Topology · Mathematics 2020-09-16 Julia E. Bergner , Charles Rezk

The space $SL(2,\mathbb{R})\times SL(2,\mathbb{R})$ admits a natural homogeneous pseudo-Riemannian nearly Kaehler structure. We investigate almost complex surfaces in this space. In particular we obtain a complete classification of the…

Differential Geometry · Mathematics 2020-06-23 Elsa Ghandour , Luc Vrancken

The homotopy coherent nerve from simplicial categories to simplicial sets and its left adjoint C are important to the study of (infinity,1)-categories because they provide a means for comparing two models of their respective homotopy…

Category Theory · Mathematics 2011-04-01 Emily Riehl

We define a category parameterizing Calabi-Yau algebra objects in an infinity category of spans. Using this category, we prove that there are equivalences of infinity categories relating, firstly: 2-Segal simplicial objects in C to algebra…

Algebraic Topology · Mathematics 2019-05-17 Walker H. Stern

We study the relations between the projective and the almost conformally symplectic structures on a smooth even dimensional manifold. We describe these relations by a single almost conformally symplectic connection with totally trace--free…

Differential Geometry · Mathematics 2017-10-17 Jan Gregorovič

We construct the smooth, compact moduli space of similarity classes of labeled, oriented triangles. The space, denoted $\mathfrak D$, is a connected sum of three projective planes, and projects via blowdown to two shape spaces that have…

Algebraic Geometry · Mathematics 2025-08-01 Eric Brussel , Madeleine Goertz , Elijah Guptill , Kelly Lyle

The purpose of this short note is to illustrate the utility of (semi-) dendroidal objects in describing certain 'up-to-homotopy' operads. Specifically, we exhibit a semi-dendroidal space satisfying the Segal condition, whose evaluation at a…

Algebraic Topology · Mathematics 2020-07-03 Philip Hackney

This thesis is divided into two parts. In the first part, we study models of $(\infty,\omega)$-categories. The main result is to establish a Quillen equivalence between Rezk's complete Segal $\Theta$-spaces and Verity's complicial sets. In…

Category Theory · Mathematics 2023-10-13 Félix Loubaton

Univalence, originally a type theoretical notion at the heart of Voevodsky's Univalent Foundations Program, has found general importance as a higher categorical property that characterizes descent and hence classifying maps in…

Category Theory · Mathematics 2022-11-15 Raffael Stenzel

In this article we introduce the notion of a k-almost-quasifibration and give many examples. We also show that a large class of these examples are not quasifibrations. As a consequence, supporting the Asphericity conjecture of [19], we…

Geometric Topology · Mathematics 2025-02-21 S K Roushon

For each $n \geq -1$, a quasi-category is said to be $n$-truncated if its hom-spaces are $(n-1)$-types. In this paper we study the model structure for $n$-truncated quasi-categories, which we prove can be constructed as the Bousfield…

Category Theory · Mathematics 2020-04-14 Alexander Campbell , Edoardo Lanari