Nicolas Ginoux, Georges Habib, Mihaela Pilca, Uwe Semmelmann
We characterize those complete K{ä}hler manifolds supporting a nonconstant real-valued function with critical points whose Hessian is complex linear, has pointwise two eigenvalues and whose gradient is a Hessian-eigenvector.
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We prove the generalized Obata theorem on foliations. Let M be a complete Riemannian manifold with a foliation F of codimension $q>1$ and a bundle-like metric. Then $(M, F)$ is transversally isometric to the q-sphere of radius 1/c in (q+1)-dimensional Euclidean space endowed with the action of a discrete subgroup of the orthogonal group O(q), if and only if there exists a non-constant basic function f such that $\nabla_X df = -c^2 f X^\flat for all basic normal vector fields X, where c is a positive constant and \nabla is the connection on the normal bundle. By the generalized Obata theorem, w…
The holonomy of the Obata connection on Joyce hypercomplex manifolds
本文研究了Joyce四复流形上Obata连接的holonomy，证明了除SU(2n+1)外，holonomy群严格包含于四元数一般线性群，并给出了SU(5)的新例子。
In this paper, we obtain several a-priori estimates for the Calabi flow on projective bundles admitting the generalized Calabi constructions.
We show that on an HKT manifold the holonomy of the Obata connection is contained in SL(n,H) if and only if the Lee form is an exact one form. As an application, we show compact HKT manifolds with holomorphically trivial canonical bundle which are not balanced. A simple criterion for non-existence of HKT metric on hypercomplex manifold is given in terms of the Ricci-type tensors of the Obata connection.
Let (M,I,J,K) be a compact hypercomplex manifold admitting an HKT-metric. Assume that the canonical bundle of (M,I) is trivial as a holomorphic line bundle. We show that the holonomy of Obata connection on M is contained in SL(n,H). In Appendix we apply these arguments to compact nilmanifolds equipped with abelian hypercomplex structures, showing that such manifolds have holonomy in SL(n,H).
Starting with an orientable compact real-analytic Riemannian manifold $(L,g)$ with $χ(L)=0$, we show that a small neighbourhood $ \textrm{Op}(L) $ of the zero section in the cotangent bundle $T^{*}L$ carries a Calabi-Yau structure such that the zero section is an isometrically embedded special Lagrangian submanifold.
In the present paper we provide a description of complete Calabi-Yau metrics on the canonical bundle of generalized complex flag manifolds. By means of Lie theory we give an explicit description of complete Ricci-flat Kähler metrics obtained through the Calabi ansatz technique. We use this approach to provide several explicit examples of noncompact complete Calabi-Yau manifolds, these examples include canonical bundles of non-toric flag manifolds (e.g. Grassmann manifolds and full flag manifolds).
We prove that the Calabi-Yau equation on the Kodaira-Thurston manifold has a unique solution for every $S^1$-invariant initial datum.
We develop a method, initially due to Salamon, to compute the space of ``invariant'' forms on an associated bundle X=P\times_G V, with a suitable notion of invariance. We determine sufficient conditions for this space to be d-closed. We apply our method to the construction of Calabi-Yau metrics on TCP^1 and TCP^2.
In the spirit of [10,2], we study the Calabi-Yau equation on $T^2$-bundles over $\mathbb{T}^2$ endowed with an invariant non-Lagrangian almost-Kähler structure showing that for $T^2$-invariant initial data it reduces to a Monge-Ampère equation having a unique solution. In this way we prove that for every total space $M^4$ of an orientable $T^2$-bundle over $\mathbb{T}^2$ endowed with an invariant almost-Kähler structure the Calabi-Yau problem has a solution for every normalized $T^2$-invariant volume form.
In this paper we present a construction of stable bundles on Calabi-Yau threefolds using the method of bundle extensions. This construction applies to any given Calabi-Yau threefold with h^{1,1}>1. We give examples of stable bundles of rank 2 and 4 constructed out of pure geometric data of the given Calabi-Yau space. As an application, we find that some of these bundles satisfy the physical constraint imposed by heterotic string anomaly cancellation.
We prove a case of the conjecture of Douglas, Reinbacher and Yau about the existence of stable vector bundles with prescribed Chern classes on a Calabi-Yau threefold. For this purpose we prove the existence of certain stable vector bundle extensions over elliptically fibered Calabi-Yau threefolds.
This note gives a simple formula for the unique asymptotically conical Calabi-Yau metrics on the canonical bundle of a flag variety known to exist by the work of R. Goto and others. This is done by generalizing the well known Calabi Ansatz to general Kähler classes. We give some examples of explicit families, in particular, a formula for the two dimensional family of asymptotically conical metrics on the canonical bundle of $F_{1,2}$.
We find sufficient conditions for a principal toric bundle over compact Kähler manifolds to admit Calabi-Yau connections with torsion. With the aids of a topological classification, we construct such geometry on $n(S^2\times S^4)#(n+1)(S^3\times S^3)$
We study an algebraic inequality for nilpotent matrices and show some interesting geometric applications: (i) obtaining topological information for nilpotent polystable Higgs bundles over a compact Riemann surface; (ii) obtaining a sharp upper bound of the holomorphic sectional curvatures of the period domain and the Hodge metric on the Calabi-Yau moduli.
We prove that a given Calabi-Yau threefold with a stable holomorphic vector bundle can be perturbed to a solution of the Strominger system provided that the second Chern class of the vector bundle is equal to the second Chern class of the tangent bundle. If the Calabi-Yau threefold has strict SU(3) holonomy then the equations of motion derived from the heterotic string effective action are also satisfied by the solutions we obtain.
Principal bundles with holomorphic connections over a Kaehler Calabi-Yau manifold
本文证明紧致Kähler Calabi-Yau流形上具有全纯联络的全纯向量丛必具有平坦全纯联络，推广了Atiyah问题与文献[BD]的结果，并应用于Cartan几何及叶状Cartan几何。
Quantizations of local Calabi-Yau threefolds and their moduli of vector bundles
本文研究局部 Calabi-Yau 三维流形的非交换形变几何，揭示 Poisson 结构选择对量子向量丛模空间几何的关键影响。
In arXiv:1008.1018 it is shown that a given stable vector bundle $V$ on a Calabi-Yau threefold $X$ which satisfies $c_2(X)=c_2(V)$ can be deformed to a solution of the Strominger system and the equations of motion of heterotic string theory. In this note we extend this result to the polystable case and construct explicit examples of polystable bundles on elliptically fibered Calabi-Yau threefolds where it applies. The polystable bundle is given by a spectral cover bundle, for the visible sector, and a suitably chosen bundle, for the hidden sector. This provides a new class of heterotic flux co…
We give a method to construct Calabi-Yau metrics on G-invariant vector bundles over Kahler coset spaces G/H using supersymmetric nonlinear realizations with matter coupling. As a concrete example we discuss the CP^N model coupled with matter. The canonical line bundle is reproduced by the singlet matter and the cotangent bundle with a new non-compact Calabi-Yau metric which is not hyper-Kahler is obtained by the anti-fundamental matter.
Numerical spectra of the Laplacian for line bundles on Calabi-Yau hypersurfaces
本文首次数值计算了Calabi-Yau三重流形上取值于线丛的Dolbeault Laplacian谱，并通过三个例子验证了算法的准确性，为弦紧致化中Yukawa耦合计算提供了必要工具。
Non-existence of Higgs fields on Calabi-Yau Manifolds
本文利用 Yang–Mills–Higgs 流证明，紧连通 Calabi–Yau 流形上 Chern 类消失的半稳定 Higgs 丛具有平凡 Higgs 场，且其底层向量丛必为半稳定。
Non-Kähler Calabi-Yau manifolds and holomorphic geometric structures
本文研究了非Kaehler紧复流形上全纯几何结构的性质，证明了Vaisman Calabi-Yau流形上所有全纯类型全纯几何结构都是局部同构的，并且如果几何结构是刚性的，则Vaisman流形必须是一个Kodaira流形。
Complete non-compact $\operatorname{Spin}(7)$-manifolds from $T^2$-bundles over AC Calabi Yau manifolds
本研究提出在渐近锥形Calabi-Yau流形的主T²丛上构造完备非紧Spin(7)流形的新方法，得到渐近T²纤维化锥形的新型无穷远几何，并构造出无穷多微分同胚型及首个完备环形Spin(7)流形实例。
Calabi-Yau metrics of Calabi type with polynomial rate of convergence
本文构造了定义在光滑反典范除子补集上、以多项式速度逼近Calabi模型空间的完备Calabi-Yau度量，并证明了其在固定上同调类中的唯一性。
We consider the minimum Yang-Mills energy on the complete $G_{2}$-manifolds and Calabi-Yau 3-folds,the connection $A$ is a stability Yang-Mills connection on the $G$-bundle $E$.We prove that the connection must be a $G_{2}$-instanton on $G_{2}$-manifold and the bundle is holomorphic on Calabi-Yau 3-fold with holonomy $SU(3)$.
The large mass limit of $G_2$ and Calabi-Yau monopoles
本文研究渐近锥形 $G_2$ 流形和 Calabi-Yau 3-fold 上 $SU(2)$ 单极子的大质量极限，给出极限结构理论，提取带 Dirac 奇异性的奇异阿贝尔单极子，并证明气泡能量恒等式。
In this note we show that if a compact Kahler manifold with trivial canonical bundle is the total space of a holomorphic fibration without singular fibers, then the fibration is a holomorphic fiber bundle. In the algebraic case, the fibration becomes trivial after a finite base change.
We prove that the first Chern form of the moduli space of polarized Calabi-Yau manifolds, with the Hodge metric or the Weil-Petersson metric, represent the first Chern class of the canonical extensions of the tangent bundle to the compactification of the moduli space with normal crossing divisors.
The Kuranishi space of joint deformations of Calabi--Yau manifolds and holomorphic vector bundles
本文研究Calabi-Yau流形与全纯向量丛的联合形变，在Fujiki流形等条件下证明无阻碍性，并构造有阻碍的例子，推广了Li-Pan和Iacono-Manetti定理，回答了Felten的两个问题。
We study the class of compact complex manifolds whose first Chern class vanishes in the Bott-Chern cohomology. This class includes all manifolds with torsion canonical bundle, but it is strictly larger. After making some elementary remarks, we show that a manifold in Fujiki's class C with vanishing first Bott-Chern class has torsion canonical bundle. We also give some examples of non-Kahler Calabi-Yau manifolds, and discuss the problem of defining and constructing canonical metrics on them.
$t$-Gauduchon Ricci-flat metrics on non-Kähler Calabi-Yau manifolds
该研究在Picard数大于1的有理齐次簇上的紧非Kähler Calabi-Yau主环面丛中，对所有t<1构造了新的t-Gauduchon Ricci平坦度量，并给出了特定Fano三维簇上主T²-丛的多种Ricci平坦及平衡Hermitian度量新实例。
In this paper we will introduce a new notion of geometric structures defined by systems of closed differential forms in term of the Clifford algebra of the direct sum of the tangent bundle and the cotangent bundle on a manifold. We develop a unified approach of a deformation problem and establish a criterion of unobstructed deformations of the structures from a cohomological point of view. We construct the moduli spaces of the structures by using the action of b-fields and show that the period map of the moduli space is locally injective under a cohomological condition (the local Torelli type …
Let $X$ be a compact connected Kähler--Einstein manifold with $c_1(TX)\, \geq\, 0$. If there is a semistable Higgs vector bundle $(E\,,θ)$ on $X$ with $θ\,\not=\,0$, then we show that $c_1(TX)=0$, any $X$ satisfying this condition is called a Calabi--Yau manifold, and it admits a Ricci--flat Kähler form \cite{Ya}. Let $(E\,,θ)$ be a polystable Higgs vector bundle on a compact Ricci--flat Kähler manifold $X$. Let $h$ be an Hermitian structure on $E$ satisfying the Yang--Mills--Higgs equation for $(E\,,θ)$. We prove that $h$ also satisfies the Yang--Mills--Higgs equation for $(E\,,0)$. A similar…
New extremal Kähler metrics on projective bundles
该研究证明射影化空间 $\boldsymbol{P}(E)$ 存在对合型兼容极端近凯勒度量等价于存在Calabi极端凯勒度量，利用对应关系简化方程，并应用于秩4向量丛的射影丛，证明其为Calabi梦想流形。
Complete Calabi-Yau metrics on noncompact abelian fibered threefolds
研究以 $\mathbb{C}$ 为底的非紧阿贝尔纤维化三维流形，构造其上的完备 Calabi-Yau 度量，并给出典范丛为负的紧化。
The heterotic $\rm{G}_2$ system on contact Calabi--Yau $7$-manifolds
本研究在Calabi-Yau 3-轨形的非平凡圆周丛全空间上构造杂化G₂系统非平凡解，通过按弦常数α'幂次调整S¹纤维得到余校准G₂-结构，找到满足无反常条件的切丛联络与G₂-瞬子示例。
We show that the Ricci flat Calabi's metrics on holomorphic line bundles over compact Kaehler-Einstein manifolds are not projectively induced. As a byproduct we solve a conjecture addressed in [arXiv:1705.03908v2 [math.DG]] by proving that any multiple of the Eguchi-Hanson metric on the blow-up of C^2 at the origin is not projectively induced.
We introduce the concept of a branched holomorphic Cartan geometry. It generalizes to higher dimension the definition of branched (flat) complex projective structure on a Riemann surface introduced by Mandelbaum. This new framework is much more flexible than that of the usual holomorphic Cartan geometries. We show that all compact complex projective manifolds admit branched flat holomorphic projective structure. We also give an example of a non-flat branched holomorphic normal projective structure on a compact complex surface. It is known that no compact complex surface admits such a structure…
We construct a class of stable SU(5) bundles on an elliptically fibered Calabi-Yau threefold with two sections, a variant of the ordinary Weierstrass fibration, which admits a free involution. The bundles are invariant under the involution, solve the topological constraint imposed by the heterotic anomaly equation and give three generations of Standard Model fermions after symmetry breaking by Wilson lines of the intermediate SU(5) GUT-group to the Standard Model gauge group. Among the solutions we find some which can be perturbed to solutions of the Strominger system. Thus these solutions pro…
We propose a construction of Kähler and non-Kähler Calabi-Yau manifolds by branched double covers of twistor spaces. In this construction we use the twistor spaces of four-manifolds with self-dual conformal structures, with the examples of connected sum of $n$ $\mathbb{P}^{2}$s. We also construct $K3$-fibered Calabi-Yau manifolds from the branched double covers of the blow-ups of the twistor spaces. These manifolds can be used in heterotic string compactifications to four dimensions. We also construct stable and polystable vector bundles. Some classes of these vector bundles can give rise to s…
Explicit complete Ricci-flat metrics and Kähler-Ricci solitons on direct sum bundles
该研究在Kähler-Einstein Fano流形上由典范根丛幂次直和构成的向量丛全空间中，利用哈密顿2-形式理论构造出多种完备Kähler-Ricci孤立子与Calabi-Yau度量，得到了具有不同体积增长特性的新几何例子。
In this paper, we prove the equivalence of the existence of extremal Kahler metrics and the properness of the modified K energy on projective bundles. Moreover, we discuss the relations of the lower boundedness of the K energy, the infimum of the Calabi energy and the extremal polynomials. In particular, we give an example where the modified K energy is bounded from below but not proper.
For a one parameter family of Calabi-Yau threefolds, Green, Griffiths and Kerr have expressed the total singularities in terms of the degrees of Hodge bundles and Euler number of the general fiber. In this paper, we show that the total singularities can be expressed by the sum of asymptotic values of BCOV invariants, studied by Fang, Lu and Yoshikawa. On the other hand, by using Yau's Schwarz lemma, we prove Arakelov type inequalities and Euler number bound for Calabi-Yau family over a compact Riemann surface.
Holomorphic linking numbers, ABC Massey products, and Calabi-Yau 3-folds
本文通过将复解析循环的 ABC 马斯奇产品与全纯链接数关联，构造出具有非消失 ABC 马斯奇产品的简单连通投影3折面族。
We introduce a homology theory whose Euler characteristics counts ASD bundles over four dimensional co-associative submanifolds in (almost) G_2 manifolds. As a TQFT, in relative situations, we have the Fukaya-Floer category of Lagrangians intersection in the moduli space of special Lagrangian submanifolds in CY threefolds.
Albanese map for Kähler manifolds with nef anticanonical bundle
本文研究具有 nef 反正则丛的 Kähler 流形的 Albanese 映射结构，证明一般纤维为 Calabi-Yau 时流形本身为 Calabi-Yau，并对 Cao–Höring 关于射影空间纤维情形的结果给出更拓扑的证明。
We prove that the deformation theory of compactifiable asymptotically cylindrical Calabi-Yau manifolds is unobstructed. This relies on a detailed study of the Dolbeault-Hodge theory and its description in terms of the cohomology of the compactification. We also show that these Calabi-Yau metrics admit a polyhomogeneous expansion at infinity, a result that we extend to asymptotically conical Calabi-Yau metrics as well. We then study the moduli space of Calabi-Yau deformations that fix the complex structure at infinity. There is a Weil-Petersson metric on this space which we show is Kähler. By p…
Let $X$ be a complex projective variety with only canonical singularities and with trivial canonical bundle. Let $L$ be an ample line bundle on $X$. Assume that the pair $(X,L)$ is the flat limit of a family of smooth polarized Calabi-Yau manifolds. Assume that for each singular point $x \in X$ there exist a Kahler-Einstein Fano manifold $Z$ and a positive integer $q$ dividing $K_Z$ such that $-\frac{1}{q}K_Z$ is very ample and such that the germ $(X,x)$ is locally analytically isomorphic to a neighborhood of the vertex of the blow-down of the zero section of $\frac{1}{q}K_{Z}$. We prove that …
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