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To every oriented tree, we associate a moduli problem for sheaves over a projective manifold $X$. We define the corresponding notion of semistability and establish the existence of moduli spaces. Applying the results to the tree *->*, we…

Algebraic Geometry · Mathematics 2007-05-23 Alexander Schmitt

By means of analytic methods the quasi-projectivity of the moduli space of algebraically polarized varieties with a not necessarily reduced complex structure is proven including the case of non-uniruled polarized varieties.

Algebraic Geometry · Mathematics 2007-05-23 Georg Schumacher , Hajime Tsuji

We discuss the projectivity of the moduli space of semistable vector bundles on a curve of genus $g\geq 2$. This is a classical result from the 1960s, obtained using geometric invariant theory. We outline a modern approach that combines the…

Algebraic Geometry · Mathematics 2023-05-01 Jarod Alper , Pieter Belmans , Daniel Bragg , Jason Liang , Tuomas Tajakka

We give a moduli-theoretic treatment of the existence and properties of moduli spaces of semistable quiver representations, avoiding methods from geometric invariant theory. Using the existence criteria of Alper--Halpern-Leistner--Heinloth,…

Algebraic Geometry · Mathematics 2026-05-06 Pieter Belmans , Chiara Damiolini , Hans Franzen , Victoria Hoskins , Svetlana Makarova , Tuomas Tajakka

We decompose each moduli space of semistable sheaves on the complex projective plane with support of dimension one and degree four into locally closed subvarieties, each subvariety being the good or geometric quotient of a set of morphisms…

Algebraic Geometry · Mathematics 2009-10-29 Jean-Marc Drezet , Mario Maican

Let k be an algebraically closed field of characteristic zero. Let f:X-->S be a flat, projective morphism of k-schemes of finite type with integral geometric fibers. We prove existence of a projective relative moduli space for semistable…

Algebraic Geometry · Mathematics 2015-03-24 Adrian Langer

Let $X$ be a projective variety over a field. In this paper, we will construct a moduli space of very ample line bundles on $X$. In doing so, we develop a generalization of Fitting ideals to complexes of sheaves on $X$. We give other…

Algebraic Geometry · Mathematics 2025-08-01 Brian Nugent

Equivariance of linear neural network layers is well studied. In this work, we relax the equivariance condition to only be true in a projective sense. We propose a way to construct a projectively equivariant neural network through building…

Computer Vision and Pattern Recognition · Computer Science 2023-12-21 Georg Bökman , Axel Flinth , Fredrik Kahl

In this expository article, we follow the work of Langer to prove the boundedness of the moduli space of semistable torsion-free sheaves over a projective variety, in any characteristic.

Algebraic Geometry · Mathematics 2021-12-08 Haoyang Guo , Sanal Shivaprasad , Dylan Spence , Yueqiao Wu

The construction for nonreduced projective moduli scheme of semistable admissible pairs is performed. We establish the relation of this moduli scheme with reduced moduli scheme built up in the previous article and prove that nonreduced…

Algebraic Geometry · Mathematics 2015-05-30 Nadezda V. Timofeeva

Using an existence criterion for good moduli spaces of Artin stacks by Alper-Fedorchuk-Smyth we construct a proper moduli space of rank two sheaves with fixed Chern classes on a given complex projective manifold that are…

Algebraic Geometry · Mathematics 2020-06-18 Daniel Greb , Matei Toma

We show that certain semistable sheaves on the projective plane with linear Hilbert polynomial are cokernels of semistable morphisms of decomposable sheaves.We exhibit certain locally closed subvarieties of moduli spaces of semistable…

Algebraic Geometry · Mathematics 2013-11-14 Mario Maican

We resolve pathological wall-crossing phenomena for moduli spaces of sheaves on higher-dimensional base manifolds. This is achieved by considering slope-semistability with respect to movable curves rather than divisors. Moreover, given a…

Algebraic Geometry · Mathematics 2018-04-19 Daniel Greb , Matei Toma

We investigate the moduli spaces of one- and two-dimensional sheaves on projective K3 and abelian surfaces that are semistable with respect to a nongeneral ample divisor with regard to the symplectic resolvability. We can exclude the…

Algebraic Geometry · Mathematics 2011-05-02 Markus Zowislok

We give a criterion for the projectivisation of a reflexive sheaf on a klt space to be induced by a projective representation of the fundamental group of the smooth locus. This criterion is then applied to give a characterisation of finite…

Algebraic Geometry · Mathematics 2022-07-25 Daniel Greb , Stefan Kebekus , Thomas Peternell

We introduce a notion of stability for sheaves with respect to several polarisations that generalises the usual notion of Gieseker-stability. We prove, under a boundedness assumption, which we show to hold on threefolds or for rank two…

Algebraic Geometry · Mathematics 2016-07-20 Daniel Greb , Julius Ross , Matei Toma

We generalise the techniques of semistable reduction for flat families of sheaves to the setting of the derived category $D^b(X)$ of coherent sheaves on a smooth projective three-fold $X$. Then we construct the moduli of PT-semistable…

Algebraic Geometry · Mathematics 2011-05-05 Jason Lo

We consider all complex projective manifolds X that satisfy at least one of the following three conditions: 1. There exists a pair $(C ,\varphi)$, where $C$ is a compact connected Riemann surface and $\varphi : C\to X$ a holomorphic map,…

Algebraic Geometry · Mathematics 2009-01-28 Indranil Biswas

Let $X$ be the wonderful compactification of a complex adjoint symmetric space $G/K$ such that $rk(G/K)=rk(G)-rk(K)$. We show how to extend equivariant vector bundles on $G/K$ to equivariant vector bundles on $X$, generated by their global…

Algebraic Geometry · Mathematics 2007-05-23 Michel Brion

We define partially ample subvarieties of projective varieties, generalizing Ottem's work on ample subvarieties, and show their ubiquity. As an application, we obtain a connectedness result for pre-images of subvarieties by morphisms,…

Algebraic Geometry · Mathematics 2018-05-21 Mihai Halic
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