Peter Gilkey, JeongHyeong Park
We use the density function of a harmonic space to obtain estimates for the eigenvalues of the Jacobi operator; when these estimates are sharp, then the harmonic space is a symmetric Osserman space.
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We prove that harmonic morphisms preserve the Jacobi operator along harmonic maps. We apply this result to prove infinitesimal and local rigidity (in the sense of Toth) of harmonic morphisms to a sphere.
We show that Jacobi fields along harmonic maps between suitable spaces preserve conformality, holomorphicity, real isotropy and complex isotropy to first order; this last being one of the key tools in the proof by Lemaire and the author of integrability of Jacobi fields along harmonic maps from the 2-sphere to the complex projective plane.
In a previous paper, we showed that any Jacobi field along a harmonic map from the 2-sphere to the complex projective plane is integrable (i.e., is tangent to a smooth variation through harmonic maps). In this paper, in contrast, we show that there are (non-full) harmonic maps from the 2-sphere to the 3-sphere and 4-sphere which have non-integrable Jacobi fields. This is particularly surprising in the case of the 3-sphere where the space of harmonic maps of any degree is a smooth manifold, each map having image in a totally geodesic 2-sphere.
Twistor methods provide a powerful tool in the study of harmonic maps and harmonic morphisms. Indeed, their use has enabled us to produce a variety of examples of harmonic morphisms defined on 4-dimensional manifolds, and a complete classification in some cases. In the first part of this work, we generalize those constructions to obtain harmonic morphisms from higher-dimensional manifolds. The use of twistor methods in the study of Jacobi fields has proved quite fruitful, leading to a series of results. In the second part of this work we give a general treatment of the relations between Jacobi…
We show that any Jacobi field along a harmonic map from the 2-sphere to the complex projective plane is integrable (i.e., is tangent to a smooth variation through harmonic maps). This provides one of the few known answers to this problem of integrability, which was raised in different contexts of geometry and analysis. It implies that the Jacobi fields form the tangent bundle to each component of the manifold of harmonic maps from $S^2$ to ${\bf C}P^2$ thus giving the nullity of any such harmonic map; it also has bearing on the behaviour of weakly harmonic $E$-minimizing maps from a 3-manifold…
In the paper, we study variation formulas for transversally harmonic maps and bi-harmonic maps, respectively. We also study the transversal Jacobi field along a map and give several relations with infinitesimal automorphisms.
This article shows that every non-isotropic harmonic 2-torus in complex projective space factors through a generalised Jacobi variety related to the spectral curve. Each map is composed of a homomorphism into the variety and a rational map off it. The same ideas allow one to construct (pluri)-harmonic maps of finite type from Euclidean space into Grassmannians and the projective unitary groups. Further, some of these maps will be purely algebraic. For maps into complex projective space the algebraic maps of the plane are always doubly periodic i.e. they yield 2-tori. The classification of all …
Here we provide refinements of the stability results of Simons and Xin, concerning the stability of Yang-Mills fields and harmonic maps respectively. The result also implies the earlier Morse index estimates for both cases.
On the equivariant stability of harmonic self-maps of cohomogeneity one manifolds
本文研究余齐性一流形上调和自映射的等变稳定性，分析相应Jacobi方程，并在球面、特殊正交群及SU(3)情形显式求解，证明球面上特定作用下恒等映射等变稳定。
Stochastic Jacobi fields along discontinuous martingales on Riemannian submanifolds
本文针对欧几里得空间子流形切丛上的不连续鞅，建立切丛上不连续半鞅的伊藤微积分，推导调和映射的导数相关性质及均值、导数公式，拓展了随机分析与几何的相关理论。
In this note we will fill out the details from the recent work of Fotiadis and Daskaloyannis in arXiv:1903.05420v3, where the harmonic maps described by Y. Shi, L. Tam and T. Y.-H. Wan (in their work Harmonic Maps on Hyperbolic spaces with Singular Boundary Value, Differential Geometry 51(1999), 551-600) are written by the use of Jacobi elliptic functions. We also prove that the harmonic maps described by J. Wang in his work (The Heat Flow and Harmonic Maps between Complete Manifolds, The Gournal of Geometric Analysis, Volume 8, Number 3, 1998, 485-514) can be written by the use of Jacobi elli…
Rotational cmc surfaces in terms of Jacobi elliptic functions
本文利用雅可比椭圆函数和Lie球面几何方法，对非欧空间形式中的旋转常平均曲率曲面进行分类，并给出双曲空间中旋转常调和平均曲率曲面的显式参数化，补全了管道线性Weingarten曲面分类的最后空白。
Let $\mathcal{N}$ be the space of Gaussian distribution functions over $\mathbb{R}$, regarded as a 2-dimensional statistical manifold parameterized by the mean $μ$ and the deviation $σ$. In this paper we show that the tangent bundle of $\mathcal{N}$, endowed with its natural Kähler structure, is the Siegel-Jacobi space appearing in the context of Number Theory and Jacobi forms. Geometrical aspects of the Siegel-Jacobi space are discussed in detail (completeness, curvature, group of holomorphic isometries, space of Kähler functions, relationship to the Jacobi group), and are related to the quan…
Connection matrices on the Siegel-Jacobi upper half space and extended Siegel-Jacobi upper half space
本文推导了Siegel-Jacobi上半空间及其扩展形式在相应Jacobi群作用下不变的度量矩阵之逆，为Berezin量子化提供基础，并给出$n=2$的显式结果。
The Jacobi-orthogonality in indefinite scalar product spaces
本文推广Jacobi正交性至不定内积空间，研究其与Osserman、Jacobi对偶的关系，证明拟Clifford张量Jacobi正交，并给出3维和4维代数曲率张量Jacobi正交的充要条件。
In this paper we prove some classification theorems of real hypersur- faces in Mn(c) satisfying certain conditions on the covariant derivative of the structure Jacobi operator. We also prove the non-existence of real hypersurfaces with Codazzi type structure Jacobi operator in Mn(c).
Improved Morse Index Stability for Sequences of Harmonic Maps from Degenerating Riemann Surfaces
研究退化黎曼面上调和映射序列的扩展Morse指数稳定性，分析能量二阶变分并确定扩展Morse指数上半连续的条件，改进了早期结果并明确指出退化颈区对极限扩展指数的贡献。
We define a Hamilton-Jacobi semigroup acting on continuous functions on a compact length space. Following a strategy of Bobkov, Gentil and Ledoux, we use some basic properties of the semigroup to study geometric inequalities related to concentration of measure. Our main results are that (1) a Talagrand inequality on a measured length space implies a global Poincare inequality and (2) if the space satisfies a doubling condition, a local Poincare inequality and a log Sobolev inequality then it also satisfies a Talagrand inequality.
The Siegel-Jacobi space is a non-symmetric homogeneous space which is very important geometrically and arithmetically. In this paper, we discuss the theory of the geometry and the arithmetic of the Siegel-Jacobi space.
Problems in the Geometry of the Siegel-Jacobi Space
本文针对非对称齐次空间 Siegel-Jacobi 空间，提出其几何中的基本问题，强调其在几何与算术中的重要性。
In this article, we investigate differential operators on the Siegel-Jacobi space that are invariant under the natural action of the Jacobi group. These invariant differential operators play an important role in the arithmetic theory of Jacobi forms of higher degree. We present some explicit invariant differential operators. We present problems which are natural. We give some new partial solutions for these natural problems.
We define certain extensions of Jacobi groups of $A_n$, prove an analogue of Chevalley Theorem for their invariants, and construct a Dubrovin Frobenius structure on it orbit space.
Linear Hamiltonians in generators of the real Jacobi group on the extended Siegel-Jacobi space and equations of motion attached
本文利用扩展Siegel-Jacobi上半空间的能量函数，推导了实Jacobi群生成元中线性Hamiltonians对应的运动方程，并分别给出了n=1和一般n的情况。
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