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We prove that K-polystable log Fano pairs have reductive automorphism groups. In fact, we deduce this statement by establishing more general results concerning the S-completeness and $\Theta$-reductivity of the moduli of K-semistable log…

Algebraic Geometry · Mathematics 2020-12-02 Jarod Alper , Harold Blum , Daniel Halpern-Leistner , Chenyang Xu

In this paper, we prove that given a flat generically smooth morphism between smooth projective varieties with $F$-pure closed fibers, if the source space is Fano, weak Fano or a variety with the nef anti-canonical divisor, then so is the…

Algebraic Geometry · Mathematics 2019-12-11 Sho Ejiri

We construct one-parameter complex analytic families whose special fibers are complete toric varieties. Under some assumptions, the general fibers of these families also become toric varieties and we can explicitly describe the…

Algebraic Geometry · Mathematics 2007-05-23 Hiroshi Sato

We study the spaces of rational curves on Fano threefolds with Gorenstein terminal singularities. We generalize the results regarding Geometric Manin's Conjecture for smooth Fano threefolds, including the classification of subvarieties with…

Algebraic Geometry · Mathematics 2025-05-23 Fumiya Okamura

Under some positivity assumptions, extension properties of rationally connected fibrations from a submanifold to its ambient variety are studied. Given a family of rational curves on a complex projective manifold X inducing a covering…

Algebraic Geometry · Mathematics 2008-03-05 Mauro C. Beltrametti , Tommaso de Fernex , Antonio Lanteri

Tian's criterion for K-stability states that a Fano variety of dimension $n$ whose alpha invariant is greater than $\frac{n}{n+1}$ is K-stable. We show that this criterion is sharp by constructing singular Fano varieties with alpha…

Algebraic Geometry · Mathematics 2020-08-06 Yuchen Liu , Ziquan Zhuang

We study local, global and local-to-global properties of threefolds with certain singularities. We prove criteria for these threefolds to be rational homology manifolds and conditions for threefolds to satisfy rational Poincar\'e duality.…

Algebraic Geometry · Mathematics 2018-04-10 Antonella Grassi , Timo Weigand , with an Appendix by V. Srinivas

We study the deformation theory of a Fano variety X with normal crossing singularities of dimension at most three. We obtain a formula for the sheaf T^1(X) of first order deformations of X in a suitable log resolution of X and its singular…

Algebraic Geometry · Mathematics 2009-07-22 Nikolaos Tziolas

In this paper we study the algebraic ranks of foliations on $\mathbb{Q}$-factorial normal projective varieties. We start by establishing a Kobayashi-Ochiai's theorem for Fano foliations in terms of algebraic rank. We then investigate the…

Algebraic Geometry · Mathematics 2023-08-22 Jie Liu

We study elliptically fibered K3 surfaces, with sections, in toric Fano threefolds which satisfy certain combinatorial properties relevant to F-theory/Heterotic duality. We show that some of these conditions are equivalent to the existence…

Algebraic Geometry · Mathematics 2012-07-11 Antonella Grassi , Vittorio Perduca

We study the K-moduli space of products of Fano varieties in relation to the product of K-moduli spaces of the product components. We show that there exists a well-defined morphism from the product of K-moduli stacks of Fano varieties to…

Algebraic Geometry · Mathematics 2024-05-15 Thedoros S. Papazachariou

We study the deformation theory of a Q-Fano 3-fold with only terminal singularities. First, we show that the Kuranishi space of a Q-Fano 3-fold is smooth. Second, we show that every Q-Fano 3-fold with only "ordinary" terminal singularities…

Algebraic Geometry · Mathematics 2014-10-30 Taro Sano

We study weighted Fano fourfolds of K3 type realized as hypersurfaces in weighted projective spaces. Under the additional assumption that the singular locus has dimension at most one, we prove that only finitely many such families exist. We…

Algebraic Geometry · Mathematics 2025-06-24 Valeria Bertini , Francesco Antonio Denisi , Enrico Fatighenti , Annalisa Grossi

We consider a class of foliations on the complex projective plane that are determined by a quadratic vector field in a fixed affine neighborhood. Such foliations, as a rule, have an invariant line at infinity. Two foliations with…

Dynamical Systems · Mathematics 2010-10-28 Yulij Ilyashenko , Vadims Moldavskis

We prove that any affine, resp. polarized projective, spherical variety admits a flat degeneration to an affine, resp. polarized projective, toric variety. Motivated by Mirror Symmetry, we give conditions for the limit toric variety to be a…

Algebraic Geometry · Mathematics 2007-05-23 Valery Alexeev , Michel Brion

We investigate birational boundedness of Fano varieties and Fano fibrations. We establish an inductive step towards birational boundedness of Fano fibrations via conjectures related to boundedness of Fano varieties and Fano fibrations. As…

Algebraic Geometry · Mathematics 2019-12-02 Chen Jiang

We show that there exist Mori fibre spaces whose total spaces are klt but bases are not. We also construct Mori fibre spaces which have relatively non-trivial torsion line bundles.

Algebraic Geometry · Mathematics 2018-10-05 Hiromu Tanaka

We classify some special classes of non-rational Fano threefolds with terminal singularities. In particular, all such hyperelliptic and trigonal varieties are found.

Algebraic Geometry · Mathematics 2019-07-15 Yuri Prokhorov

The Chow-Mumford (CM) line bundle is a functorial line bundle on the base of any family of klt Fano varieties. It is conjectured that it yields a polarization on the moduli space of K-poly-stable klt Fano varieties. Proving ampleness of the…

Algebraic Geometry · Mathematics 2020-09-01 Giulio Codogni , Zsolt Patakfalvi

The goal of this work is to study geometric properties of geometrically irreducible subschemes on degenerations of Fano varieties (more generally, of separably rationally connected varieties). It is known that these geometrically…

Algebraic Geometry · Mathematics 2024-09-17 Santai Qu