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We study the failure of the Lipman-Zariski conjecture in positive characteristic. For rational double points, the conjecture holds true except for a short finite list of exceptions. For log canonical surface singularities, the conjecture…

Algebraic Geometry · Mathematics 2022-05-09 Patrick Graf

We study the singularities of the secant variety $\Sigma(X,L)$ associated to a smooth variety $X$ embedded by a sufficiently positive adjoint bundle $L$. We show that $\Sigma(X,L)$ is always Du Bois singular. Examples of secant varieties…

Algebraic Geometry · Mathematics 2017-02-02 Chih-Chi Chou , Lei Song

The present paper is concerned with differential forms on log canonical varieties. It is shown that any p-form defined on the smooth locus of a variety with canonical or klt singularities extends regularly to any resolution of…

Algebraic Geometry · Mathematics 2015-03-13 Daniel Greb , Stefan Kebekus , Sandor J. Kovacs , Thomas Peternell

Let $X$ be a $n$-dimensional smooth projective variety and $L$ be an ample Cartier divisor on $X$. We conjecture that a very general element of the linear system $|K_X+(3n+1)L|$ is a hyperbolic algebraic variety. This conjecture holds for…

Algebraic Geometry · Mathematics 2025-05-05 Joaquín Moraga , Wern Yeong

We prove that the higher direct images $R^qf_*\Omega^p_{\mathcal Y/S}$ of the sheaves of relative K\"ahler differentials are locally free and compatible with arbitrary base change for flat proper families whose fibers have $k$-Du Bois local…

Algebraic Geometry · Mathematics 2025-09-10 Robert Friedman , Radu Laza

We prove the Lipman-Zariski conjecture for complex surface singularities of genus one, and also for those of genus two whose link is not a rational homology sphere. As an application, we characterize complex $2$-tori as the only normal…

Algebraic Geometry · Mathematics 2021-05-07 Patrick Graf

We study the problem of smoothing Fano and Calabi-Yau varieties with isolated Du Bois lci singularities. For Fano varieties, we show that any such $Y$ admits a deformation to a Fano variety with only $1$-rational singularities, and if none…

Algebraic Geometry · Mathematics 2026-05-07 Anda Tenie

We study the Du Bois complex $\underline{\Omega}_Z^\bullet$ of a hypersurface $Z$ in a smooth complex algebraic variety in terms its minimal exponent $\widetilde{\alpha}(Z)$. The latter is an invariant of singularities, defined as the…

Algebraic Geometry · Mathematics 2022-07-06 Mircea Mustata , Sebastian Olano , Mihnea Popa , Jakub Witaszek

Let $X$ be a compact K\"ahler fourfold with klt singularities and vanishing first Chern class, smooth in codimension two. We show that $X$ admits a Beauville-Bogomolov decomposition: a finite quasi-\'etale cover of $X$ splits as a product…

Algebraic Geometry · Mathematics 2024-06-04 Patrick Graf

Let X be a surface whose Cox ring has a single relation satisfying moreover a kind of linearity property. Under a simple assumption, we show that the geometric Manin's conjectures hold for some degrees lying in the dual of the effective…

Algebraic Geometry · Mathematics 2012-05-17 David Bourqui

Let $X$ be a projective variety over an algebraically closed field $k$ of arbitrary characteristic $p \ge 0$. A surjective endomorphism $f$ of $X$ is $q$-polarized if $f^\ast H \sim qH$ for some ample Cartier divisor $H$ and integer $q >…

Algebraic Geometry · Mathematics 2021-10-22 Paolo Cascini , Sheng Meng , De-Qi Zhang

A $\mathbb Q$-conic bundle is a proper morphism from a threefold with only terminal singularities to a normal surface such that fibers are connected and the anti-canonical divisor is relatively ample. We study the structure of $\mathbb…

Algebraic Geometry · Mathematics 2010-04-26 Shigefumi Mori , Yuri Prokhorov

Given a logarithmic $1$-form on the snc locus of a log canonical surface pair $(X, D)$ over a perfect field of characteristic $p \ge 7$, we show that it extends with at worst logarithmic poles to any resolution of singularities. We also…

Algebraic Geometry · Mathematics 2022-01-19 Patrick Graf

Given an ambient variety $X$ and a fixed subvariety $Z$ we give sufficient conditions for the existence of a boundary $\Delta$ such that $Z$ is a log canonical center for the pair $(X, \Delta)$. We also show that under some additional…

Algebraic Geometry · Mathematics 2015-12-02 Lorenzo Prelli

We study a natural generalization of transversally intersecting smooth hypersurfaces in a complex manifold: hypersurfaces, whose components intersect in a transversal way but may be themselves singular. Such hypersurfaces will be called…

Algebraic Geometry · Mathematics 2018-05-02 Eleonore Faber

For X a compact Riemann surface of positive genus, the strange duality conjecture predicts that the space of sections of certain theta bundle on moduli of bundles of rank r and level k is naturally dual to a similar space of sections of…

Algebraic Geometry · Mathematics 2007-05-23 Prakash Belkale

Let $X$ be a normal projective variety admitting a polarized endomorphism $f$, i.e., $f^*H\sim qH$ for some ample divisor $H$ and integer $q>1$. Then Broustet and Gongyo proposed the conjecture that $X$ is of Calabi-Yau type (CY for short),…

Algebraic Geometry · Mathematics 2025-09-23 Wentao Chang , De-Qi Zhang

We extend the notions of higher Du Bois and higher rational singularities to pairs in the sense of the minimal model program. We extend numerous results to these higher pairs, including Bertini type theorems, stability under finite maps and…

Algebraic Geometry · Mathematics 2026-03-12 Haoming Ning , Brian Nugent

We consider the following conjecture: if X is a smooth projective variety over a field of characteristic zero, then there is a dense set of reductions X_s of X to positive characteristic such that the action of the Frobenius morphism on the…

Commutative Algebra · Mathematics 2011-06-02 Mircea Mustata , Vasudevan Srinivas

In this paper we study a notion of volume for Cartier divisors on arbitrary blow-ups of normal complex algebraic varieties of dimension greater than one, with a distinguished point. We apply this to study a volume for normal isolated…

Algebraic Geometry · Mathematics 2011-05-17 Mihai Fulger