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It is conjectured that the moduli b-divisor of the Kawamata-Kodaira canonical bundle formula associated to a klt-trivial fibration $(X,B)\to Z$ is semi-ample. In this paper, we show the semi-ampleness of an arbitrarily small perturbation of…

Algebraic Geometry · Mathematics 2012-07-18 Caucher Birkar , Yifei Chen

In this paper we prove two results about the rational chain connectedness for klt threefolds with anti-big canonical divisors in the relative setting.

Algebraic Geometry · Mathematics 2018-02-28 Yuan Wang

A proof based on reduction to finite fields of Esnault-Viehweg's stronger version of Sommese Vanishing Theorem for $k$-ample line bundles is given. This result is used to give different proofs of isotriviality results of A. Parshin and L.…

Algebraic Geometry · Mathematics 2007-05-23 Mark Andrea A. de Cataldo

We prove that a weak $\mathbb{Q}$-Fano $3$-fold with terminal singularities has unobstructed deformations. By using this result and computing some invariants of a terminal singularity, we provide two results on global deformation of a weak…

Algebraic Geometry · Mathematics 2017-09-12 Taro Sano

We prove combination theorems in the spirit of Klein and Maskit in the context of discrete convergence groups acting geometrically finitely on their limit sets. As special cases, we obtain combination theorems for geometrically finite…

Group Theory · Mathematics 2023-05-16 Alec Traaseth , Theodore Weisman

We describe an action of the concordance group of knots in the three-sphere on concordances of knots in arbitrary 3-manifolds. As an application we define the notion of almost-concordance between knots. After some basic results, we prove…

Geometric Topology · Mathematics 2018-03-07 Daniele Celoria

We study the classifying space B Diff(M) of the diffeomorphism group of a connected, compact, orientable 3-manifold M. In the case that M is reducible we build a contractible space parametrising the systems of reducing spheres. We use this…

Geometric Topology · Mathematics 2024-04-22 Rachael Boyd , Corey Bregman , Jan Steinebrunner

We prove a local rigidity result for infinitesimally rigid capillary surfaces in some Riemannian $3$-manifolds with mean convex boundary. We also derive bounds on the genus, number of boundary components and area of any compact two-sided…

Differential Geometry · Mathematics 2021-04-13 Eduardo Longa

We give a proof of Mukai's Theorem on the existence of certain exceptional vector bundles on prime Fano threefolds. To our knowledge this is the first complete proof in the literature. The result is essential for Mukai's biregular…

Algebraic Geometry · Mathematics 2025-09-26 Arend Bayer , Alexander Kuznetsov , Emanuele Macrì

We show that tensor products of semiample vector bundles are semiample. For k-ampleness in the sens of Sommese, we show that over compact complex manifolds tensor products of semiample and k-ample vector bundles are k-ample, and the sum of…

Algebraic Geometry · Mathematics 2016-07-26 F. Laytimi , W. Nahm

We obtain a sufficient condition for a Fano threefold with terminal singularities to have a conic bundle structure.

Algebraic Geometry · Mathematics 2022-02-02 Yuri Prokhorov

In this paper we generalize the Local Removable Singularity Theorem in [16] for minimal laminations to the case of weak $H$-laminations (with $H\in \mathbb{R}$ constant) in a punctured ball of a Riemannian three-manifold. We also obtain a…

Differential Geometry · Mathematics 2014-01-14 William H. Meeks , Joaquin Perez , Antonio Ros

This note surveys recent progress toward the profinite rigidity of orientable finite-volume hyperbolic 3-manifolds. Beginning in a brief review of some basic settings of profinite completion and rigidity of general groups, we state the…

Geometric Topology · Mathematics 2025-08-29 Tianwei Liu

In this paper, we use canonical bundle formulas to prove some generalizations of an old theorem of Kawamata on the semiampleness of nef and abundant log canonical divisors. In particular, we show that for klt pairs $(X,B)$ with $K_X+B$…

Algebraic Geometry · Mathematics 2022-09-07 Priyankur Chaudhuri

Canonical bundle formula due to Kawamata and others has played fundamental roles in algebraic geometry. We show that the canonical bundle formula has analytic characterization in terms of fiberwise integration, which confirms a folklore…

Algebraic Geometry · Mathematics 2025-08-25 Dano Kim

We give a simple construction of new, complete, finite volume manifolds $M$ of bounded, nonpositive curvature. These manifolds have ends that look like a mixture of locally symmetric ends of different ranks and their fundamental groups are…

Geometric Topology · Mathematics 2021-03-17 Grigori Avramidi , T. Tam Nguyen Phan

We give degree lower bounds for quotient line bundles of the lowest piece of a Hodge module induced by a complex variation of Hodge structures outside a simple normal crossing divisor, beyond the unipotent variation case. This note aims to…

Algebraic Geometry · Mathematics 2026-05-14 Ze Yun

We investigate the combinatorial analogues, in the context of normal surfaces, of taut and transversely measured (codimension 1) foliations of 3-manifolds. We establish that the existence of certain combinatorial structures, a priori weaker…

Geometric Topology · Mathematics 2007-05-23 Danny Calegari

For a K3 surface over a field of characteristic 2 which is finitely generated over its prime subfield, we prove that the cokernel of the natural map from the Brauer group of the base field to that of the K3 surface is finite modulo the…

Number Theory · Mathematics 2018-01-08 Kazuhiro Ito

In this article, we show that, for any compact 3-manifold, there is a $C^{1}$ volume-minimizing one-dimensional foliation. More generally, we show the existence of mass-minimizing rectifiable sections of sphere bundles without isolated…

Differential Geometry · Mathematics 2007-05-23 David L. Johnson , Penelope Smith