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In this paper, we pose several conjectures on structures and images of maximal rationally connected fibrations of smooth projective varieties admitting semi-positive holomorphic sectional curvature. Toward these conjectures, we prove that…

Differential Geometry · Mathematics 2022-05-24 Shin-ichi Matsumura

The projective shape of a configuration of k points or "landmarks" in RP(d) consists of the information that is invariant under projective transformations and hence is reconstructable from uncalibrated camera views. Mathematically, the…

Statistics Theory · Mathematics 2018-11-06 Thomas Hotz , Florian Kelma , John T. Kent

E. Cartan's method of moving frames is applied to 3-dimensional manifolds $M$ which are CR-embedded in 5-dimensional real hyperquadrics $Q$ in order to classify $M$ up to CR symmetries of $Q$ given by the action of one of the Lie groups…

Differential Geometry · Mathematics 2021-02-23 Curtis Porter

We recall the complex structure on the generalised loop spaces $W^{k,2}(S,X)$, where $S$ is a compact real manifold with boundary and $X$ is a complex manifold, and prove a Hartogs-type extension theorem for holomorphic maps from certain…

Complex Variables · Mathematics 2025-01-28 Mohammed Anakkar

Via the transverse Hilbert scheme construction, we associate a holomorphic completely integrable system to a surface $S$ endowed with a holomorphic symplectic form $\omega$ and a projection onto $\mathbb{C}$. We provide a full…

Differential Geometry · Mathematics 2018-01-22 Niccolò Lora Lamia Donin

We establish a parametric extension $h$-principle for overtwisted contact structures on manifolds of all dimensions, which is the direct generalization of the $3$-dimensional result from \cite{Eli89}. It implies, in particular, that any…

Symplectic Geometry · Mathematics 2014-10-14 Matthew Strom Borman , Yakov Eliashberg , Emmy Murphy

We construct k-parameter families of rational surface automorphisms for any k. These are automorphisms of surfaces X, which are constructed from iterated blowups over the projective plane. In certain cases: we are able to determine the…

Complex Variables · Mathematics 2009-02-28 Eric Bedford , Kyounghee Kim

We show that for any k>1, stratified sets of finite complexity are insufficient to realize all homology classes of codimension k in all smooth manifolds. We also prove a similar result concerning smooth generic maps whose double-point sets…

Algebraic Topology · Mathematics 2014-03-07 Mark Grant , Andras Szucs

We consider possibly singular rational projective k*-surfaces and provide an explicit description of the unit component of the automorphism group in terms of isotropy group orders and intersection numbers of suitable invariant curves. As an…

Algebraic Geometry · Mathematics 2020-12-02 Juergen Hausen , Timo Hummel

We study symplectic structures on K\"ahler surfaces with p_g = 0. We give an example of a projective surface which admits a symplectic structure which is not compatible with any K\"ahler metric.

Symplectic Geometry · Mathematics 2010-12-17 Paolo Cascini , Dmitri Panov

We show that $U(k)$-invariant hypercomplex structures on (open subsets) of regular semisimple adjoint orbits in $\mathfrak{gl}(k,{\mathbb C})$ correspond to algebraic curves $C$ of genus $(k-1)^2$, equipped with a flat projection…

Differential Geometry · Mathematics 2022-01-14 Roger Bielawski

CR singularities of real 4-submanifolds in complex 3-space are classified by using local holomorphic coordinate changes to transform the quadratic coefficients of the real analytic defining equation into a normal form. The quadratic…

Complex Variables · Mathematics 2009-04-21 Adam Coffman

Fibrations methods which were previously used for complex homogeneous spaces and CR-homogenous spaces of special types ([HO1], [AHR], [HR],[R]}) are developed in a general framework. These include the $\lie g$-anticanonical fibration in the…

Complex Variables · Mathematics 2008-08-16 B. Gilligan , A. Huckleberry

We introduced a new coordinate-free approach to study the Cauchy-Riemann (CR) maps between the real hyperquadrics in the complex projective space. The central theme is based on a notion of orthogonality on the projective space induced by…

Complex Variables · Mathematics 2021-10-11 Yun Gao , Sui-Chung Ng

For a very general polarized $K3$ surface $S\subset \mathbb{P}^g$ of genus $g\ge 5$, we study the linear system on the Hilbert square $S^{[2]}$ parametrizing quadrics in $\mathbb{P}^g$ that contain $S$. We prove its very ampleness for…

Algebraic Geometry · Mathematics 2025-10-03 Ángel David Ríos Ortiz , Andrés Rojas , Jieao Song

A global representation is a compatible collection of representations of the outer automorphism groups of the groups belonging to some collection of finite groups $\mathscr{U}$. Global representations assemble into an abelian category…

Representation Theory · Mathematics 2026-05-20 Miguel Barrero , Tobias Barthel , Luca Pol , Neil Strickland , Jordan Williamson

We present some fundamental facts about a class of generalized K\"ahler structures defined by invariant complex structures on compact Lie groups. The main computational tool is the BH-to-GK spectral sequences that relate the bi-Hermitian…

Differential Geometry · Mathematics 2015-01-06 Shengda Hu

Let ${\bold M}_0$ be a compact, regular q-pseudoconcave compact CR submanifold of a complex manifold ${\bold G}$ and ${\cal B}$ - a holomorphic vector bundle on ${\bold G}$ such that $\dim H^r({\bold M}_0, {\cal B}\big|_{\bold M})=0$ for…

Complex Variables · Mathematics 2007-05-23 Peter Polyakov

We consider holomorphic foliations by curves on compact complex manifolds, for which we investigate the existence of projective structures along the leaves varying holomorphically (foliated projective structures), that satisfy particular…

Complex Variables · Mathematics 2026-01-13 Bertrand Deroin , Adolfo Guillot

A complex filling of a CR manifold is said to be equivariant with respect to a CR action if the action extends to a smooth action by biholomorphisms on the whole filling. Under a noncompactness condition for the action, we describe all…

Differential Geometry · Mathematics 2009-01-05 Benoit Kloeckner