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The Hopf conjecture states that an even-dimensional, positively curved Riemannian manifold has positive Euler characteristic. We prove this conjecture under the additional assumption that a torus acts by isometries and has dimension bounded…

Differential Geometry · Mathematics 2016-01-20 Lee Kennard

The celebrated union-closed conjecture is concerned with the cardinalities of various subsets of the Boolean $d$-cube. The cardinality of such a set is equivalent, up to a constant, to its measure under the uniform distribution, so we can…

Combinatorics · Mathematics 2025-11-05 Gabriel Gendler

We propose singular variants of the Singer-Hopf conjecture, formulated in terms of the Euler-Mather characteristic, intersection homology Euler characteristic and, resp., virtual Euler characteristic of a closed irreducible subvariety of an…

Algebraic Geometry · Mathematics 2022-03-22 Laurentiu Maxim

The following conjecture arose out of discussions between B. Harbourne, J. Ro\'e, C. Cilberto and R. Miranda: for a smooth projective surface $X$ there exists a positive constant $c_X$ such that $h^1(\mathcal O_X(C))\le c_X h^0(\mathcal…

Algebraic Geometry · Mathematics 2020-02-13 Sichen Li

We give a concrete expression of a minimal singular metric of a big line bundle on a compact K\"ahler manifold which is the total space of a toric bundle over a complex torus. In this class of manifolds, Nakayama constructed examples which…

Algebraic Geometry · Mathematics 2014-06-05 Takayuki Koike

In this paper, we obtain two extension theorems for cohomology classes and holomorphic sections defined on analytic subvarieties, which are defined as the supports of the quotient sheaves of multiplier ideal sheaves of…

Complex Variables · Mathematics 2019-09-20 Xiangyu Zhou , Langfeng Zhu

For almost all Riemannian metrics (in the $C^\infty$ Baire sense) on a closed manifold $M^{n+1}$, $3\leq (n+1)\leq 7$, we prove that the union of all closed, smooth, embedded minimal hypersurfaces is dense. This implies there are infinitely…

Differential Geometry · Mathematics 2018-02-12 Kei Irie , Fernando C. Marques , André Neves

A long-standing conjecture in complex geometry says that a compact Hermitian manifold with constant holomorphic sectional curvature must be K\"ahler when the constant is non-zero and must be Chern flat when the constant is zero. The…

Differential Geometry · Mathematics 2023-02-24 Peipei Rao , Fangyang Zheng

Rigidity results are obtained for Riemannian $d$-manifolds with $\sec \geqslant 1$ and spherical rank at least $d-2>0$. Conjecturally, all such manifolds are locally isometric to a round sphere or complex projective space with the…

Differential Geometry · Mathematics 2014-09-29 Benjamin Schmidt , Krishnan Shankar , Ralf Spatzier

We prove that the multiplication of sections of globally generated line bundles on a model wonderful variety M of simply connected type is always surjective. This follows by a general argument which works for every wonderful variety and…

Algebraic Geometry · Mathematics 2018-06-26 Paolo Bravi , Jacopo Gandini , Andrea Maffei

We provide a sharp monotonicity theorem about the distribution of subharmonic functions on manifolds, which can be regarded as a new, measure theoretic form of the uncertainty principle. As an illustration of the scope of this result, we…

Classical Analysis and ODEs · Mathematics 2025-11-11 Aleksei Kulikov , Fabio Nicola , Joaquim Ortega-Cerdà , Paolo Tilli

Some curvature properties of Kahler manifolds of indefinite metrics are studied. Analogues of a Kulkarni's theorem are proved for such manifolds.

Differential Geometry · Mathematics 2010-08-12 Ognian Kassabov , Adrijan Borisov

Let $\mathcal{O}_K$ be the ring of integers in an algebraic number field $K$ and let $S:=\operatorname{Spec}(\mathcal{O}_K)$. Let $T_0,\ldots,T_n$ be regular schemes of finite type over $S$ and let $X$ be a scheme of finite type over $T_n$…

Algebraic Geometry · Mathematics 2020-11-11 Helge Øystein Maakestad

A theorem by Mumford implies that every automorphic line bundle on a pure open Shimura variety, equipped with an invariant smooth metric, can be uniquely extended as a line bundle on a toroidal compactification of the variety, in such a way…

Algebraic Geometry · Mathematics 2014-05-14 José Burgos , Ulf Kühn , Jürg Kramer

We prove an obstruction at the level of rational cohomology in small degrees to the existence of positively curved metrics with large symmetry rank. The symmetry rank bound is logarithmic in the dimension of the manifold. As an application,…

Differential Geometry · Mathematics 2012-09-21 Lee Kennard

We study the existence of canonical K\"ahler metrics on the projectivisation of strictly Mumford semistable holomorphic vector bundles over a complex curve. We also provide an algebro-geometric characterization of these metrics.

Differential Geometry · Mathematics 2017-05-17 Julien Keller

This is a survey of results, both classical and recent, on behaviour of plurisubharmonic functions near their $-\infty$-points, together with the related topics for positive closed currents.

Complex Variables · Mathematics 2007-05-23 Alexander Rashkovskii

We generalize the Demailly approximation theorem from complex geometry to Arakelov geometry.As an application, let $X/\mathbb{Q}$ be an integral projective variety and $\overline N$ be an adelic line bundle on $X$, we prove that…

Number Theory · Mathematics 2023-04-13 Binggang Qu , Hang Yin

Beauville asked if a compact K\"ahler manifold with split tangent bundle has a universal covering that is a product of manifolds. We use Mori theory and elementary results about holomorphic foliations to study this problem for projective…

Algebraic Geometry · Mathematics 2017-11-10 Andreas Höring

The generalized Lax conjecture asserts that each hyperbolicity cone is a linear slice of the cone of positive semidefinite matrices. We prove the conjecture for a multivariate generalization of the matching polynomial. This is further…

Combinatorics · Mathematics 2016-11-21 Nima Amini