Beniamino Cappelletti-Montano, Antonio De Nicola, Ivan Yudin
We study a natural class of LCK manifolds that we call integrable LCK manifolds: those where the anti-Lee form $η$ corresponds to an integrable distribution. As an application we obtain a characterization of unimodular integrable LCK Lie algebras as Kähler Lie algebras equipped with suitable derivations.
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A locally conformally Kähler (LCK) manifold is a manifold which is covered by a Kähler manifold, with the deck transform group acting by homotheties. We show that the search for LCK metrics on Oeljeklaus-Toma manifolds leads to a (yet another) variation on Kronecker's theorem on units. In turn, this implies that on Oeljeklaus-Toma manifold associated to number fields with $2t$ complex embeddings and $s$ real embeddings with $s<t$ there is no LCK metric.
Conformal vector fields on lcK manifolds
本文证明了紧致lcK流形上的任意共形向量场关于Gauduchon度量是Killing的，且在Kähler覆盖既非平坦也非hyperkähler时该向量场是全纯的。
We prove that any compact homogeneous locally conformally Kähler manifold has parallel Lee form.
We show that for $n>2$ a compact locally conformally Kähler manifold $(M^{2n},g,J)$ carrying a non-trivial parallel vector field is either Vaisman, or globally conformally Kähler, determined in an explicit way by some compact Kähler manifold of dimension $2n-2$.
Futaki invariant on lcK manifolds with potential
本文证明 Futaki 不变量在紧致具有势的局部共形 Kähler 流形上恒为零，解决了 Ornea 和 Verbitsky 提出的问题。
Compact homogeneous locally conformally Kahler manifolds are Vaisman. A new proof
本文证明了任意齐次LCK流形容许具LCK势的度量，并以此给出了紧致齐次LCK流形是Vaisman流形的新证明。
LcK structures with holomorphic Lee vector field on Vaisman-type manifolds
本研究完整刻画了Vaisman型紧复流形上带全纯Lee向量场的局部共形Kähler（lcK）结构，给出Lee向量场不相似于Vaisman结构Lee向量场的实例，并推广证明紧复流形上带势的全纯Lee向量场lcK度量存在正且沿反Lee向量场不变的势。
We prove that a compact toric locally conformally Kähler manifold which is not Kähler admits a toric Vaisman structure, a fact which was conjectured in \cite{mmp}. This is the final step leading to the classification of compact toric locally conformally Kähler manifolds started in \cite{p} and \cite{mmp}. We also show, by constructing an example, that unlike in the symplectic case, toric locally conformally symplectic manifolds are not necessarily toric locally conformally Kähler.
Let $M$ be a complex manifold and $L$ an oriented real line bundle on M equipped with a flat connection. An LCK ("locally conformally Kahler") form is a closed, positive (1,1)-form taking values in L, and an LCK manifold is one which admits an LCK form. Locally, any LCK form is expressed as an L-valued pluri-Laplacian of a function called LCK potential. We consider a manifold $M$ with an LCK form admitting a global LCK potential, and prove that M admits a global, positive LCK potential. Then M admits a holomorphic embedding to a Hopf manifold.
We investigate the relation between holomorphic torus actions on complex manifolds of LCK type and the existence of special LCK metrics. We show that if the group of biholomorphisms of such a manifold $(M,J)$ contains a non-real compact torus, then there exists a Vaisman metric on the manifold. Moreover, we show that if the group of biholomorphisms contains a compact torus whose dimension is half the real dimension of $M$, then $(M,J)$ admits an LCK metric with positive potential. As an application, we obtain a classification of manifolds of LCK type among all the manifolds having the structur…
An LCK manifold with potential is a compact quotient of a Kahler manifold $X$ equipped with a positive Kahler potential $f$, such that the monodromy group acts on $X$ by holomorphic homotheties and multiplies $f$ by a character. The LCK rank is the rank of the image of this character, considered as a function from the monodromy group to real numbers. We prove that an LCK manifold with potential can have any rank between 1 and $b_1(M)$. Moreover, LCK manifolds with proper potential (ones with rank 1) are dense. Two errata to our previous work are given in the last Section.
A recent result of M. Kourganoff states that if $D$ is a closed, reducible, non-flat, Weyl connection on a compact conformal manifold $M$, then the universal covering of $M$, endowed with the metric whose Levi-Civita covariant derivative is the pull-back of $D$, is isometric to $\mathbb{R}^q\times N$ for some irreducible, incomplete Riemannian manifold $N$. Moreover, he characterized the case where the dimension of $N$ is $2$ by showing that $M$ is then a mapping torus of some Anosov diffeomorphism of $T^{q+1}$. We show that in this case one necessarily has $q=1$ or $q=2$.
Do products of compact complex manifolds admit LCK metrics?
针对紧复流形乘积被猜想不容许 LCK 结构的问题，本文将已知紧 LCK 流形分为带势、Inoue 型和含有理曲线三类，并证明 LCK 流形与任一类中流形的乘积均无 LCK 结构。
A locally conformally Kähler (lcK) manifold is a complex manifold $(M,J)$ together with a Hermitian metric $g$ which is conformal to a Kähler metric in the neighbourhood of each point. In this paper we obtain three classification results in locally conformally Kähler geometry. The first one is the classification of conformal classes on compact manifolds containing two non-homothetic Kähler metrics. The second one is the classification of compact Einstein locally conformally Kähler manifolds. The third result is the classification of the possible (restricted) Riemannian holonomy groups of compa…
A note on locally conformally Kaehler structures and small deformations of Hopf manifolds
本文通过构造对角型Hopf流形附近的复解析族，结合lcK势在小参数复解析族中保持的已知结论，证明了所有Hopf流形都容许局部共形Kaehler结构。
Calabi-Yau locally conformally Kähler manifolds
本文研究了Calabi-Yau局部共形Kähler流形，证明此类流形必为Vaisman流形，并探讨了其与Kodaira流形的关系。
Lee classes on LCK manifolds with potential
本文研究带势 LCK 流形的 Lee 类，证明其集合构成 $H^1(M,\mathbb R)$ 中的开半空间，并为 Vaisman 情形下 Tsukada 的结果提供新的自足证明。
A locally conformally Kähler (LCK) manifold is a complex manifold covered by a Kähler manifold, with the covering group acting by homotheties. We show that if such a compact manifold X admits a holomorphic submersion with positive dimensional fibers at least one of which is of Kähler type, then X is globally conformally Kähler or biholomorphic, up to finite covers, to a Vaisman manifold (i.e. a mapping torus over a circle, with Sasakian fibre). As a consequence, we show that the product between a compact non-Kähler LCK and a compact Kähler manifold cannot carry a LCK metric.
We show a bijective correspondence between compact toric locally conformally symplectic manifolds which admit a compatible complex structure and pairs $(C,a)$, where $C$ is a good cone in the dual Lie algebra of the torus and $a$ is a positive real number. Moreover, we prove that any toric locally conformally Kähler metric on a compact manifold admits a positive potential.
A locally conformally Kahler (LCK) manifold is a complex manifold with a Kahler structure on its covering and the deck transform group acting on it by holomorphic homotheties. One could think of an LCK manifold as of a complex manifold with a Kahler form taking values in a local system $L$, called the conformal weight bundle. The $L$-valued cohomology of $M$ is called Morse-Novikov cohomology. It was conjectured that (just as it happens for Kahler manifolds) the Morse-Novikov complex satisfies the $dd^c$-lemma. If true, it would have far-reaching consequences for the geometry of LCK manifolds.…
Compact balanced threefolds and LCK manifolds with constant holomorphic sectional curvature
该研究验证了$c\leq0$时紧致平衡三维簇满足埃尔米特几何中关于常陈全纯截面曲率的长期猜想，还将该猜想推广到典范度量联络情形并对连通紧致LCK流形成立。
Compact lcK manifolds with Gauduchon parallel vector fields
该研究刻画了紧局部共形Kähler流形上Gauduchon平行向量场与度量类型的关系，通过Bismut和乐群表征紧Vaisman流形，并得出复二维时∇^(1/3)-平行向量场对度量的约束结论。
An locally conformally Kahler (LCK) manifold with potential is a complex manifold with a cover which admits an automorphic Kahler potential. An LCK manifold with potential can be embedded to a Hopf manifold, if its dimension is at least 3. We give a functional-analytic proof of this result based on Riesz-Schauder theorem and Montel theorem. We give an alternative argument for complex surfaces, deducing embedding theorem from the Spherical Shell Conjecture.
A locally conformally Kähler (LCK) manifold $M$ is one which is covered by a Kähler manifold $\tilde M$ with the deck transform group acting conformally on $\tilde M$. If $M$ admits a holomorphic flow, acting on $\tilde M$ conformally, it is called a Vaisman manifold. Neither the class of LCK manifolds nor that of Vaisman manifolds is stable under small deformations. We define a new class of LCK-manifolds, called LCK manifolds with potential, which is closed under small deformations. All Vaisman manifolds are LCK with potential. We show that an LCK-manifold with potential admits a covering whi…
We show that Oeljeklaus-Toma manifolds $X(K, U)$ where $K$ is a number field of signature $(s, t)$ such that $s\geq 1,$ $t\geq 2$ and $s\geq 2t$ admit no lck metric. Combined with the earlier results by K. Oeljeklaus - M. Toma and A. Dubickas this completely solves the problem of existence of LCK metrics on Oeljeklaus-Toma manifolds.
We prove that a compact lcK manifold with holomorphic Lee vector field is Vaisman provided that either the Lee field has constant norm or the metric is Gauduchon (i.e., the Lee field is divergence-free). We also give examples of compact lcK manifolds with holomorphic Lee vector field which are not Vaisman.
On products of locally conformally Kähler manifolds
本文证明了正维紧复流形的乘积不存在严格局部共形Kähler度量，解决了lcK几何中长期未解的猜想。
Bimeromorphic geometry of LCK manifolds
本文研究Kähler形式在最小Kähler覆盖上恰当时的LCK流形，证明其任意双亚纯映射均为全纯映射，从而具有唯一极小模型，并适用于Hopf流形、复子流形及OT流形。
Functionals for the Study of LCK Metrics on Compact Complex Manifolds
本文通过引入并研究一种随流形复维数（2或更高）而异的泛函，为紧复流形上局部共形Kähler度量的存在性问题提供了新的研究方法。
p-lck with potential structure on LVMB manifolds
本文将 lck 结果推广至 LVMB 流形，刻画带势 lck 流形的稀缺性，构造反例否定 p≥m−1 猜想，并提出在假设 (H) 下 N 为带势 1-lck 的新猜想。
Vaisman's theorem for locally conformally Kähler (lcK) compact manifolds states that any lcK metric on a compact complex manifold which admits a Kähler metric is, in fact, globally conformally Kähler (gcK). In this paper, we extend this theorem to compact complex spaces with singularities.
In this article we introduce a generalization of locally conformally Kaehler metrics from complex manifolds to complex analytic spaces with singularities and study which properties of locally conformally Kaehler manifolds still hold in this new setting. We prove that if a complex analytic space has only quotient singularities, then it admits a locally conformally Kaehler metric if and only if its universal cover admits a Kaehler metric such that the deck automorphisms act by homotheties of the Kaehler metric. We also prove that the blow-up at a point of a LCK complex space is also LCK.
A Hermitian structure on a manifold is called locally conformally Kähler (LCK) if it locally admits a conformal change which is Kähler. In this survey we review recent results of invariant LCK structures on solvmanifolds and present original results regarding the canonical bundle of solvmanifolds equipped with a Vaisman structure, that is, a LCK structure whose associated Lee form is parallel.
A manifold M is locally conformally Kahler (LCK) if it admits a Kahler covering with monodromy acting by holomorphic homotheties. For a compact connected group G acting on an LCK manifold by holomorphic automorphisms, an averaging procedure gives a G-invariant LCK metric. Suppose that U(1) acts on an LCK manifold M by holomorphic isometries, and the lifting of this action to the Kahler cover of M is not isometric. We show that the cover admits an automorphic Kahler potential, and hence can be embedded to a Hopf manifold.
Locally conformally Kahler (LCK) manifolds with potential are those which admit a Kahler covering with a proper, automorphic Kaehler potential. Existence of a potential can be characterized cohomologically as a vanishing of a certain cohomology class, called the Bott-Chern class. Compact LCK manifolds with potential are stable at small deformations and admit holomorphic embeddings into Hopf manifolds. This class strictly includes the Vaisman manifolds. We show that every compact LCK manifold with potential can be deformed into a Vaisman manifold. Therefore, every such manifold is diffeomorphic…
On LCK Geometry of Gauduchon Connections
本文研究Gauduchon联络在LCK和Vaisman流形中的适用性，通过相关问题与条件确定Bismut联络是最优选择，并研究其在Hopf流形上的对应方程与结构刻画。
A locally conformally Kahler (LCK) manifold is a manifold which is covered by a Kahler manifold, with the deck transform group acting by homotheties. We show that the blow-up of a compact LCK manifold along a complex submanifold admits an LCK structure if and only if this submanifold is globally conformally Kahler. We also prove that a twistor space (of a compact 4-manifold, a quaternion-Kahler manifold or a Riemannian m anifold) cannot admit an LCK metric, unless it is Kahler.
Algebraic cones of LCK manifolds with potential
本文研究可嵌入 Hopf 流形的带位势 LCK 流形，证明其 $\Z$-覆盖为代数锥，且仿射代数结构不依赖原流形选择，并给出等价的内蕴定义。
A locally conformally Kahler (LCK) manifold is a complex manifold admitting a Kahler covering, with the monodromy acting on this covering by homotheties. We define three cohomology invariants, the Lee class, the Morse-Novikov class, and the Bott-Chern class, of an LCK-structure. These invariants together play the same role as the Kahler class in Kahler geometry. If these classes for two LCK-structures coincide, the difference between these structures can be expressed by a smooth potential, similar to the Kahler case. We show that the Morse-Novikov class and the Bott-Chern class of a Vaisman ma…
Locally Conformally Kähler Manifolds of Algebraic Codimension One
研究代数余维数为1的紧致局部共形Kähler流形，证明其双亚纯于等平凡椭圆纤维化全空间，且存在一个变更双亚纯支配具有椭圆曲线自由作用的流形。
Balanced metrics and Gauduchon cone of locally conformally Kahler manifolds
本文研究了局部共形Kahler流形的度量性质，提出并部分证明了容许平衡、SKT与LCK三种Hermitian形式中两种的紧复流形必容许Kahler度量的猜想，同时证明了关于Bott--Chern同调的猜想并验证了所有已知LCK流形。
An LCK manifold with potential is a compact quotient M of a Kahler manifold X equipped with a positive plurisubharmonic function f, such that the monodromy group acts on $X$ by holomorphic homotheties and maps f to a function proportional to f. It is known that M admits an LCK potential if and only if it can be holomorphically embedded to a Hopf manifold. We prove that any non-Vaisman LCK manifold with potential contains a complex surface with normalization biholomorphic to a Hopf surface H. Moreover, H can be chosen non-diagonal, hence, also not admitting a Vaisman structure.
A locally conformally Kahler (LCK) manifold is a complex manifold admitting a Kahler covering M, such that its monodromy acts on this covering by homotheties. A compact LCK manifold is called LCK with potential if M admits an authomorphic Kahler potential. It is known that in this case it is an algebraic cone, that is, the set of all non-zero vectors in the total space of an anti-ample line bundle over a projective orbifold. We start with an algebraic cone C, and show that the set of Kahler metrics with potential which could arise from an LCK structure is in bijective correspondence with the s…
Oeljeklaus-Toma (OT) manifolds are complex non-Kähler manifolds whose construction arises from specific number fields. In this note, we compute their de Rham cohomology in terms of invariants associated to the background number field. This is done by two distinct approaches, one using invariant cohomology and the other one using the Leray-Serre spectral sequence. In addition, we compute also their Morse-Novikov cohomology. As an application, we show that the low degree Chern classes of any complex vector bundle on an OT manifold vanish in the real cohomology. Other applications concern the OT …
A manifold $M$ is locally conformally Kahler (LCK) if it admits a Kahler covering with monodromy acting by holomorphic homotheties. Let $M$ be an LCK manifold admitting a holomorphic conformal flow of diffeomorphisms, lifted to a non-isometric homothetic flow on its covering. We show that $M$ admits an automorphic potential. This version was added 10 years after publication to correct some errors in the original.
A locally conformally Kähler (LCK) manifold is a complex manifold whose universal cover is Kähler with monodromy group acting on the universal cover by holomorphic homotheties. A Vaisman manifold $M$ is a compact non-Kähler LCK manifold admitting an action of a holomorphic conformal flow lifting to an action on a Kähler cover by nontrivial homotheties. When the orbits of the action on $M$ are compact, it is known that every stable holomorphic vector bundle over $M$, $\dim(M) \geq 3$, is equivariant and filtrable. In the present paper we generalize this result to irregular Vaisman manifolds.
A locally conformally Kaehler (LCK) manifold is a complex manifold admitting a Kaehler covering M, with monodromy acting on M by Kaehler homotheties. A compact LCK manifold is Vaisman if it admits a holomorphic flow acting by non-trivial homotheties on M. We prove a non-Kaehler analogue of Kodaira embedding theorem: any compact Vaisman manifold admits a natural holomorphic immersion to a Hopf manifold. As an application, we obtain that any Sasakian manifold has a contact immersion to an odd-dimensional sphere.
Principles of Locally Conformally Kahler Geometry
本书系统介绍 LCK 流形的几何原理、研究现状、习题与开放问题，面向复几何方向研究生。
We classify and investigate locally conformally Kähler structures on four-dimensional solvable Lie algebras up to linear equivalence. As an application we can produce many examples in higher dimension, here including lcK structures on Oeljeklaus-Toma manifolds, and we also give a geometric interpretation of some of the $4$-dimensional structures in our classification.
It is well known that cohomology of any non-trivial 1-dimensional local system on a nilmanifold vanishes (this result is due to L. Alaniya). A complex nilmanifold is a quotient of a nilpotent Lie group equipped with a left-invariant complex structure by an action of a discrete, co-compact subgroup. We prove a Dolbeault version of Alaniya's theorem, showing that the Dolbeault cohomology of a nilpotent Lie algebra with coefficients in any non-trivial 1-dimensional local system vanishes. Note that the Dolbeault cohomology of the corresponding local system on the manifold is not necessarily zero. …
On the Classification of Vaisman Manifolds with Vanishing First Basic Chern Class and Large First Betti Number
本文研究了第一贝蒷数较大且第一基本陈类消失的瓦伊斯曼流形，证明其与柯代拉-图尔金流形同胚，并探讨了其复结构、特征叶状结构及阿贝尔映射关联，进一步讨论了基本调和1形式长度恒定条件下的同胚性和复结构特性，以及与横贯几何形式化的联系。
Special structures on almost abelian solvmanifolds
通过三元组表示刻画带有可积复结构的几乎阿贝尔李代数，并分类具有p-凯勒或p-多重闭结构的李代数，包括凯勒、平衡、多重闭和高杜雄度量。
In this paper we construct a new class of surfaces whose geodesic flow is integrable (in the sense of Liouville). We do so by generalizing the notion of tubes about curves to 3-dimensional manifolds, and using Jacobi fields we derive conditions under which the metric of the generalized tubular sub-manifold admits an ignorable coordinate. Some examples are given, demonstrating that these special surfaces can be quite elaborate and varied.
Deformations of the scalar curvature of a partially integrable pseudohermitian manifold
本文类比 Riemannian 流形上的 Fischer–Marsden 理论，研究部分可积伪 Hermitian 流形的标量曲率形变，提出 $R$-奇异空间并建立稳定性条件与部分无穷小刚性结果。
In the present paper, we show that the geometry of a screen integrable null hypersurface can be generated from an isometric immersion of a leaf of its screen distribution into the ambient space. We prove, under certain geometric conditions, that such immersions are contained in semi-Euclidean spheres or hyperbolic spaces, and the underlying null hypersurfaces are necessarily umbilic and screen totally umbilic. Where necessary, examples have been given to illustrate the main ideas.
Integrable Geodesic Flows on Cones over Riemannian Manifolds
本文研究了锥面上的测地流，证明其超积分性及可积性，受Birkhoff弹道研究启发。
We prove that an integrable system over a symplectic manifold, whose symplectic form is covariantly constant w.r.t. the Gauss-Manin connection, carries a natural hyper-symplectic structure. Moreover, a special Kaehler structure is induced on the base manifold.
Completely Integrable Gradient System on the bivariate beta statistical manifold
本文研究三参数双变量beta统计流形上的完全可积梯度系统，证明其哈密顿性与Lax对表示，并利用Stirling近似揭示其伪黎曼几何与梯度流的线性化，凸显信息几何与动力系统的关联。
We introduce integrable complex structures on twistor spaces fibered over complex manifolds. We then show, in particular, that the twistor spaces associated with generalized Kahler, SKT and strong HKT manifolds all naturally admit complex structures. Moreover, in the strong HKT case we construct a metric and three compatible complex structures on the twistor space that have equal torsions.
We discuss a recurrent geometrical method, due to Élie Cartan and von Weber ([1],[11]) enabling us to determine, step by step, the maximal integral manifolds of a not necessarily integrable nor regular Pfaffian system. The dimensions of such integral manifolds can, of course, vary from point to point but more so can vary at a given point it depending upon the choice of their recurrent buildup. When the system is regular and integrable then, of course, we obtain the maximal integral leaves of the integral foliation. Attention is also given to those integrable systems that can be integrated by q…
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