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We consider the question of extending a smooth homotopy coherent finite cyclic group action on the boundary of a smooth 4-manifold to its interior. As a result, we prove that Dehn twists along any Seifert homology sphere, except the…

Geometric Topology · Mathematics 2024-09-27 Sungkyung Kang , JungHwan Park , Masaki Taniguchi

We give a complex polarized variation of Hodge structure over a compact K"ahler manifold $M$ which controls all finite-dimensional complex polarized variations of Hodge structure over $M$ and their tensor relations. As a corollary, we…

Algebraic Geometry · Mathematics 2022-07-25 Hisashi Kasuya

In this paper, we first generalize to any hyper-K\"ahler manifold with nonzero third Betti number results proved by O'Grady for hyper-K\"ahler manifolds of generalized Kummer type. In the second part, we restrict to hyper-K\"ahler manifolds…

Algebraic Geometry · Mathematics 2022-08-23 Claire Voisin

We show that the number of equivariant deformation classes of real structures in a given deformation class of compact hyperkahler manifolds is finite.

Algebraic Geometry · Mathematics 2008-03-21 Alex Degtyarev , Ilia Itenberg , Viatcheslav Kharlamov

The nearly K\"{a}hler structures on the 6-sphere, as a twistor bundle sections are researched. We show that for any point of twistor bundle there exists an 1-parametric family of sections, passing through the point, which give nearly…

Differential Geometry · Mathematics 2015-10-19 N. A. Daurtseva

We are concerned in this article with a classical question in spectral geometry dating back to McKean-Singer, Patodi and Tanno: whether or not the constancy of holomorphic sectional curvature of a complex $n$-dimensional compact K\"ahler…

Differential Geometry · Mathematics 2018-04-03 Ping Li

Let H be a 4 dimensional almost Hermitian manifold which satisfies the Kaehler identity. Then H is complex Osserman if and only if H has constant holomorphic sectional curvature. We also classify in arbitrary dimensions all the complex…

Differential Geometry · Mathematics 2010-03-30 Miguel Brozos-Vazquez , Peter Gilkey

Singular fibrations generalize achiral Lefschetz fibrations of 4-manifolds over surfaces while sharing some of their properties. For instance, relatively minimal singular fibrations are determined by their monodromy. We explain how to…

Geometric Topology · Mathematics 2024-04-24 Louis Funar

We propose that under certain conditions heterotic string compactifications on half-flat and nearly-Kahler manifolds are equivalent. Based on this correspondence we argue that the moduli space of the nearly-Kahler manifolds under discussion…

High Energy Physics - Theory · Physics 2009-11-10 Andrei Micu

We construct examples of complete quaternionic K\"ahler manifolds with an end of finite volume, which are not locally homogeneous. The manifolds are aspherical with fundamental group which is up to an infinite cyclic extension a semi-direct…

Differential Geometry · Mathematics 2022-12-23 V. Cortés , M. Röser , D. Thung

This paper first studies the regularity of conformal homeomorphisms on smooth locally embeddable strongly pseudoconvex CR manifolds. Then moduli of curve families are used to estimate the maximal dilatations of quasiconformal…

Complex Variables · Mathematics 2009-09-25 Puqi Tang

For compact K\"ahlerian manifolds, the holomorphic pseudosymmetry reduces to the local symmetry if additionally the scalar curvature is constant and the structure function is non-negative. Similarly, the holomorphic Ricci-pseudosymmetry…

Differential Geometry · Mathematics 2010-11-18 Zbigniew Olszak

In this short note we prove that the number of deformation types of compact hyperkaehler manifolds with prescribed second cohomology and second Chern class is finite. The proof uses the finiteness result of Kollar and Matsusaka, a formula…

Algebraic Geometry · Mathematics 2007-05-23 Daniel Huybrechts

We study the K\"ahler geometry of stage n Bott manifolds, which can be viewed as $n$-dimensional generalizations of Hirzebruch surfaces. We show, using a simple induction argument and the generalized Calabi construction from…

Differential Geometry · Mathematics 2020-12-17 Charles P. Boyer , David M. J. Calderbank , Christina W. Tønnesen-Friedman

This article reveals a significant connection in geometry: when the Lee form $\theta$ is normal to an almost Hermitian manifold $N$, it implies that $N$ possesses a nearly K\"ahler structure. Investigating locally conformally Spin(7)…

Differential Geometry · Mathematics 2024-03-04 Eyup Yalcinkaya

This paper concerns the explicit construction of extremal Kaehler metrics on total spaces of projective bundles, which have been studied in many places. We present a unified approach, motivated by the theory of hamiltonian 2-forms (as…

Differential Geometry · Mathematics 2015-06-26 Vestislav Apostolov , David M. J. Calderbank , Paul Gauduchon , Christina W. Tonnesen-Friedman

If a (possibly finite) compact Lie group acts effectively, locally linearly, and homologically trivially on a closed, simply-connected four-manifold with second Betti number at least three, then it must be isomorphic to a subgroup of S^1 x…

Geometric Topology · Mathematics 2007-07-26 Michael P. McCooey

We complete the classification of order $5$ nonsymplectic automorphisms on hyper-K\"ahler fourfolds deformation equivalent to the Hilbert square of a K3 surface. We then compute the topological Lefschetz number of natural automorphisms of…

Algebraic Geometry · Mathematics 2020-01-16 Samuel Boissière , Marc Nieper-Wißkirchen , Kévin Tari

There is a sequence of positive numbers $\delta_{2n}$, such that for any connected $2n$-dimensional Riemannian manifold $M$, there are two mutually exclusive possibilities: $1)$ There is a complex structure on $M$ making it into a K\"ahler…

Differential Geometry · Mathematics 2018-02-20 Scott O. Wilson , Mahmoud Zeinalian

We classify simply connected rationally elliptic manifolds of dimension five and those of dimension six with small Betti numbers from the point of view of their rational cohomology structure. We also prove that a geometrically formal…

Algebraic Topology · Mathematics 2016-01-22 Svjetlana Terzic