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Using Galois descent tools, we extend the Altmann-Hausen presentation of normal affine algebraic varieties endowed with an effective torus action over an algebraically closed field of characteristic zero to the case where the ground field…

Algebraic Geometry · Mathematics 2022-08-03 Pierre-Alexandre Gillard

In this paper, we show the convexity of the image of a moment map on a transverse symplectic manifold equipped with a torus action under a certain condition. We also study properties of moment maps in the case of transverse K\"ahler…

Complex Variables · Mathematics 2015-09-15 Hiroaki Ishida

We classify Fano threefolds with only terminal singularities whose canonical class is Cartier and divisible by 2, and satisfying an additional assumption that the $G$-invariant part of the Weil divisor class group is of rank 1 with respect…

Algebraic Geometry · Mathematics 2013-08-06 Yuri Prokhorov

We present some applications of the deformation theory of toric Fano varieties to K-(semi/poly)stability of Fano varieties. First, we present two examples of K-polystable toric Fano 3-fold with obstructed deformations. In one case, the…

Algebraic Geometry · Mathematics 2021-09-02 Anne-Sophie Kaloghiros , Andrea Petracci

We give some rationality constructions for Fano threefolds with canonical Gorenstein singularities.

Algebraic Geometry · Mathematics 2010-05-04 Yuri G. Prokhorov

We study unirationality of actions of finite groups on Fano threefolds.

Algebraic Geometry · Mathematics 2025-02-28 Ivan Cheltsov , Yuri Tschinkel , Zhijia Zhang

We describe the closed cone of moving curves of smooth Fano three- and fourfolds by giving finitely many equations that cut out the cone. The equations are induced by the exceptional divisors of divisorial contractions and by nef divisors…

Algebraic Geometry · Mathematics 2009-02-03 Sammy Barkowski

We prove the LeBrun-Salamon Conjecture in low dimensions. More precisely, we show that a contact Fano manifold X of dimension 2n+1 that has reductive automorphism group of rank at least n-2 is necessarily homogeneous. This implies that any…

Algebraic Geometry · Mathematics 2020-09-15 Jarosław Buczyński , Jarosław A. Wiśniewski , Andrzej Weber

Let M be a closed orientable irreducible 3-manifold, and let f be a diffeomorphism over M. We call an embedded 2-torus T an Anosov torus if it is invariant and the induced action of f over \pi_1(T) is hyperbolic. We prove that only few…

Dynamical Systems · Mathematics 2010-11-16 F. Rodriguez Hertz , J. Rodriguez Hertz , R. Ures

We present a combinatorial criterion on reflexive polytopes of dimension 3 which gives a local-to-global obstruction for the smoothability of the corresponding Fano toric threefolds. As a result, we show examples of singular Gorenstein Fano…

Algebraic Geometry · Mathematics 2021-09-02 Andrea Petracci

The anticanonical complex is a combinatorial tool that was invented to extend the features of the Fano polytope from toric geometry to wider classes of varieties. In this note we show that the Gorenstein index of Fano varieties with torus…

Algebraic Geometry · Mathematics 2024-09-06 Philipp Iber , Eva Reinert , Milena Wrobel

We compute global log canonical thresholds, or equivalently alpha invariants, of birationally rigid orbifold Fano threefolds embedded in weighted projective spaces as codimension two or three. As an important application, we prove that most…

Algebraic Geometry · Mathematics 2016-04-04 In-Kyun Kim , Takuzo Okada , Joonyeong Won

Let $X$ be a Fano threefold and $\C ^* \times X\rightarrow X$ an algebraic action. Then $X$ has a $S^1$-invariant K\"ahler structure and the corresponding $S^1$-action admits an equivariant moment map which is at the same time a perfect…

Algebraic Geometry · Mathematics 2015-08-20 Qilin Yang , Dan Zaffran

We show exceptionality of certain families of non-quasismooth weighted hypersurfaces. In particular these admit K\"ahler-Einstein metrics. Our examples are produced by the monomials generating the complex deformations of orbifolds whose…

Algebraic Geometry · Mathematics 2026-02-17 Jaime Cuadros Valle , Joe Lope Vicente

We classify the smooth Fano 4-folds of Picard number two that have a general hypersurface Cox ring.

Algebraic Geometry · Mathematics 2025-07-01 Juergen Hausen , Antonio Laface , Christian Mauz

We show that some important classes of weak Fano $3$-folds of Picard rank $2$ do not satisfy Bott vanishing. Using this we show that any smooth projective $3$-fold $X$ of Picard rank $2$ with $-K_X$ nef which is the image of a projective…

Algebraic Geometry · Mathematics 2025-09-05 Supravat Sarkar

In this note we study Fano threefolds with noncyclic torsion in the divisor class group. Since they can all be obtained as quotients of Fano threefolds, we get also all examples that can be obtained as quotients of low codimension Fanos in…

Algebraic Geometry · Mathematics 2007-06-14 Jorge Caravantes

In this work we provide effective bounds and classification results for rational $\QQ$-factorial Fano varieties with a complexity-one torus action and Picard number one depending on the invariants dimension and Picard index. This…

Algebraic Geometry · Mathematics 2012-11-26 Elaine Herppich

This article settles the question of existence of smooth weak Fano threefolds of Picard number two with small anti-canonical map and previously classified numerical invariants obtained by blowing up certain curves on smooth Fano threefolds…

Algebraic Geometry · Mathematics 2015-02-10 Maxim Arap , Joseph Cutrone , Nicholas Marshburn

In a work of Costa and Mir\'{o}-Roig state the following conjecture: Every smooth complete toric Fano variety has a full strongly exceptional collection of line bundles. The goal of this article is to prove it for toric Fano 3-folds.

Algebraic Geometry · Mathematics 2010-12-30 Alessandro Bernardi , Sofia Tirabassi