A four dimensional example of Ricci-flat metric admitting almost-Kähler non-Káhler structure

Local obstructions to projective surfaces admitting skew-symmetric Ricci tensor

The equation determining whether a projective structure admits a connection in its given projective class that has skew-symmetric Ricci tensor is an overdetermined system of semi-linear partial differential equations which we call the projective Einstein-Weyl (pEW) equation. In 2-dimensions, we give local obstructions for projective surfaces to admit such a connection in its projective class. The obstructions are the resultants of polynomial equations that have to be satisfied for there to admit any pEW solution.

Ricci solitons in almost $f$-cosymplectic manifolds

In this article we study an almost $f$-cosymplectic manifold admitting a Ricci soliton. We first prove that there do not exist Ricci solitons on an almost cosymplectic $(κ,μ)$-manifold. Further, we consider an almost $f$-cosymplectic manifold admitting a Ricci soliton whose potential vector field is the Reeb vector field and show that a three dimesional almost $f$-cosymplectic is a cosymplectic manifold. Finally we classify a three dimensional $η$-Einstein almost $f$-cosymplectic manifold admitting a Ricci soliton.

Some Properties of Kenmotsu Manifolds Admitting a Semi-symmetric Non-metric Connection

The aim of this paper is to study generalized recurrent, generalized Ricci-recurrent, weakly symmetric and weakly Ricci-symmetric Kenmotsu manifolds with respect to the semi-symmetric non-metric connection.

Almost Kenmotsu metric as Ricci-Yamabe soliton

The object of the present paper is to characterize two classes of almost Kenmotsu manifolds admitting Ricci-Yamabe soliton. It is shown that a $(k,μ)'$-almost Kenmotsu manifold admitting a Ricci-Yamabe soliton or gradient Ricci-Yamabe soliton is locally isometric to the Riemannian product $\mathbb{H}^{n+1}(-4) \times \mathbb{R}^n$. For the later case, the potential vector field is pointwise collinear with the Reeb vector field. Also, a $(k,μ)$-almost Kenmotsu manifold admitting certain Ricci-Yamabe soliton with the curvature property $Q \cdot P = 0$ is locally isometric to the hyperbolic space…

On Ricci negative Lie groups

We give an overview of what is known on Lie groups admitting a left-invariant metric of negative Ricci curvature, including many natural questions and conjectures in the solvable case. We also introduce an open and convex cone C(n) of derivations attached to each nilpotent Lie algebra n, which is defined as the image of certain moment map and parametrizes a set of solvable Lie algebras with nilradical n admitting Ricci negative metrics.

单侧D型里奇平坦多中心度量

One-sided type-D Ricci-flat multi-centre metrics

本文基于LeBrun–Tod ansatz的Tod ansatz简化形式构造单侧D型里奇平坦多中心度量，系统研究其结构并结合多孤子解方案得出相关孤子数结论，推测结论对一般中心数成立。

On Ricci flows with closed and smooth tangent flows

In this paper, we consider Ricci flows admitting closed and smooth tangent flows in the sense of Bamler [Bam20c]. The tangent flow in question can be either a tangent flow at infinity for an ancient Ricci flow, or a tangent flow at a singular point for a Ricci flow developing a finite-time singularity. Among other things, we prove: (1) that in these cases the tangent flow must be unique, (2) that if a Ricci flow with finite-time singularity has a closed singularity model, then the singularity is of Type I and the singularity model is the tangent flow at the singular point; this answers a quest…

Contact 3-manifolds and Ricci solitons

A contact 3-manifold $M$ admitting a transversal Ricci soliton $(g,v,λ)$ is either Sasakian or locally isometric to one of the Lie groups SU(2), $SL(2,R)$, E(2), E(1,1) with a left invariant metric.

On pseudo-Hermitian Einstein spaces

We describe and construct here pseudo-Hermitian structures $θ$ without torsion (i.e. with transversal symmetry) whose Webster-Ricci curvature tensor is a constant multiple of the exterior differential $dθ$. We call these structures pseudo-Hermitian Einstein and our result states that they all can be derived locally from K{ä}hler-Einstein metrics. Moreover, we discuss the corresponding Fefferman metrics of the pseudo-Hermitian Einstein structures. These Fefferman metrics are never Einstein, but they are locally always conformally Einstein.

Levi-Civita Ricci-flat metrics on compact complex manifolds

In this paper, we study the geometry of compact complex manifolds with Levi-Civita Ricci-flat metrics and prove that compact complex surfaces admitting Levi-Civita Ricci-flat metrics are Kahler Calabi-Yau surfaces or Hopf surfaces.

一类由Ricci张量和度量决定的广义Killing旋量

A class of generalised Killing spinors determined by the Ricci tensor and the metric

本文引入仿射Killing旋量（AKS），在调和曲率和局部共形平坦条件下分类允许AKS的黎曼自旋流形，刻画带平行1-形式的流形，并证明三维曲率齐次流形的局部齐次性及Bianchi度量的完整分类。

$\ast$-$η$-Ricci-Yamabe solitons on $α$-Cosymplectic manifolds with a quarter-symmetric metric connection

The goal of the present paper is to deliberate certain types of metric such as $*$-$η$-Ricci-Yamabe soliton on $α$-Cosymplectic manifolds with respect to quarter-symmetric metric connection. Further, we have proved some curvature properties of $α$-Cosymplectic manifolds admitting quarter-symmetric metric connection. Here, we have shown the characteristics of the soliton when the manifold satisfies quarter-symmetric metric connection on $α$-Cosymplectic manifolds. Later, we have acquired Laplace equation from $*$-$η$-Ricci-Yamabe soliton equation when the potential vector field $ξ$ of the solit…

关于不朽齐次 Ricci 流的等距群

On the Isometry Group of Immortal Homogeneous Ricci Flows

本文研究非紧齐次流形上不朽齐次 Ricci 流解的等距群，并给出其结构性结论。

K-接触流形上具有半对称非度量联络的若干几何孤子

K-contact manifolds admitting some geometric solitons with Semi-Symmetric Non-Metric Connection

本文研究K-接触流形上具有半对称非度量联络的几何性质，引入相关向量场，探讨Riemann、共形Ricci及共形$\eta$-Ricci-Yamabe孤子，并给出流形为多种半对称的充要条件。

Real hypersurfaces with $^{*}$-Ricci solitons of non-flat complex space forms

Kaimakamis and Panagiotidou in \cite{KP} introduced the notion of $^*$-Ricci soliton and studied the real hypersurfaces of a non-flat complex space form admitting a $^*$-Ricci soliton whose potential vector field is the structure vector field. In this article, we consider that a real hypersurface of a non-flat complex space form admits a $^*$-Ricci soliton whose potential vector field belongs to the principal curvature space and the holomorphic distribution.

静态时空上的几乎梯度里奇孤子

Almost Gradient Ricci Solitons on Static Spacetime

本文研究静态时空上几乎梯度里奇孤子的几何性质，确定其存在条件，证明在真空静态时空下退化为稳态孤子，并探讨膨胀孤子满足薛定谔方程、能量条件及底流形为爱因斯坦流形等结果。

Certain results on Kenmotsu pseudo-metric manifolds

In this paper, a systematic study of Kenmotsu pseudo-metric manifolds are introduced. After studying the properties of this manifolds, we provide necessary and sufficient condition for Kenmotsu pseudo-metric manifold to have constant $φ$-sectional curvature, and prove the structure theorem for $ξ$-conformally flat and $φ$-conformally flat Kenmotsu pseudo-metric manifolds. Next, we consider Ricci solitons on this manifolds. In particular, we prove that an $η$-Einstein Kenmotsu pseudo-metric manifold of dimension higher than 3 admitting a Ricci soliton is Einstein, and a Kenmotsu pseudo-metric 3…

Extremal Kaehler-Einstein metric for two-dimensional convex bodies

Given a convex body $K \subset \mathbb{R}^n$ with the barycenter at the origin we consider the corresponding K{ä}hler-Einstein equation $e^{-Φ} = \det D^2 Φ$. If $K$ is a simplex, then the Ricci tensor of the Hessian metric $D^2 Φ$ is constant and equals $\frac{n-1}{4(n+1)}$. We conjecture that the Ricci tensor of $D^2 Φ$ for arbitrary $K$ is uniformly bounded by $\frac{n-1}{4(n+1)}$ and verify this conjecture in the two-dimensional case. The general case remains open.

Curvature Blow-up in Doubly-warped Product Metrics Evolving by Ricci Flow

For any manifold $N^p$ admitting an Einstein metric with positive Einstein constant, we study the behavior of the Ricci flow on high-dimensional products $M = N^p \times S^{q+1}$ with doubly-warped product metrics. In particular, we provide a rigorous construction of local, type II, conical singularity formation on such spaces. It is shown that for any $k > 1$ there exists a solution with curvature blow-up rate $\| Rm \|_{\infty} (t) \gtrsim (T-t)^{-k}$ with singularity modeled on a Ricci-flat cone at parabolic scales.

$η$- Ricci Solitons on Kenmotsu manifold with Generalized Symmetric Metric Connection

The objective of the present paper is to study the $η$-Ricci solitons on Kenmotsu manifold with generalized symmetric metric connection of type $(α,β)$. There are discussed Ricci and $η$-Ricci solitons with generalized symmetric metric connection of type $(α,β)$ satisfying the conditions $\bar{R}.\bar{S}=0$, $\bar{S}.\bar{R}=0$, $\bar{W_{2}}.\bar{S}=0$ and $\bar{S}.\bar{W_{2}}=0.$. Finally, we construct an example of Kenmotsu manifold with generalized symmetric metric connection of type $(α,β)$ admitting $η$-Ricci solitons.

$η-$Ricci solitons on contact pseudo-metric manifolds

In this paper, we prove that a Sasakian pseudo-metric manifold which admits an $η-$Ricci soliton is an $η-$Einstein manifold, and if the potential vector field of the $η-$Ricci soliton is not a Killing vector field then the manifold is $\mathcal{D}-$homothetically fixed, and the vector field leaves the structure tensor field invariant. Next, we prove that a $K-$contact pseudo-metric manifold with a gradient $η-$Ricci soliton metric is $η-$Einstein. Moreover, we study contact pseudo-metric manifolds admitting an $η-$Ricci soliton with a potential vector field point-wise colinear with the Reeb v…

Weyl structures with positive Ricci tensor

We prove the vanishing of the first Betti number on compact manifolds admitting a Weyl structure whose Ricci tensor satisfies certain positivity conditions, thus obtaining a Bochner-type vanishing theorem in Weyl geometry. We also study compact Hermitian-Weyl manifolds with non-negative symmetric part of the Ricci tensor of the canonical Weyl connection and show that every such manifold has first Betti number $b_1 =1$ and Hodge numbers $h^{p,0} =0$ for $p>0$, $h^{0,1} =1$, $h^{0,q} =0$ for $q>1$.

Minimal complex surfaces with Levi-Civita Ricci-flat metrics

This is a continuation of our previous paper [14]. In [14], we introduced the first Aeppli-Chern class on compact complex manifolds, and proved that the $(1,1)$ curvature form of the Levi-Civita connection represents the first Aeppli-Chern class which is a natural link between Riemannian geometry and complex geometry. In this paper, we study the geometry of compact complex manifolds with Levi-Civita Ricci-flat metrics and classify minimal complex surfaces with Levi-Civita Ricci-flat metrics. More precisely, we show that minimal complex surfaces admitting Levi-Civita Ricci-flat metrics are Kähl…

Twistor theory of hyper-K{ä}hler metrics with hidden symmetries

We briefly review the hierarchy for the hyper-Kähler equations and define a notion of symmetry for solutions of this hierarchy. A four-dimensional hyper-Kähler metric admits a hidden symmetry if it embeds into a hierarchy with a symmetry. It is shown that a hyper-Kähler metric admits a hidden symmetry if it admits a certain Killing spinor. We show that if the hidden symmetry is tri-holomorphic, then this is equivalent to requiring symmetry along a higher time and the hidden symmetry determines a `twistor group' action as introduced by Bielawski \cite{B00}. This leads to a construction for the …

$*$-Conformal $η$-Ricci soliton within the framework of Kenmotsu manifolds

The goal of our present paper is to deliberate $*$-conformal $η$-Ricci soliton within the framework of Kenmotsu manifolds. Here we have shown that a Kenmotsu metric as a $*$-conformal $η$-Ricci soliton is Einstein metric if the soliton vector field is contact. Further, we have evolved the characterization of the Kenmotsu manifold or the nature of the potential vector field when the manifold satisfies gradient almost $*$-conformal $η$-Ricci soliton. Next, we have contrived $*$-conformal $η$-Ricci soliton admitting $(κ,μ)^\prime$-almost Kenmotsu manifold and proved that the manifold is Ricci fla…

Negative Ricci curvature on some non-solvable Lie groups II

We construct many examples of Lie groups with compact Levi factor admitting a left-invariant metric with negative Ricci curvature. We start with a Lie algebra with Levi factor su(n) or so(n) acting on an abelian nilradical via the representation on the space of homogeneous polynomials. In the case of su(2) we obtain a more general construction where the nilradical can be any nilpotent Lie algebra. We also prove a general result in the case when the Levi factor is a semisimple Lie algebra of non-compact type.

Almost Kenmotsu Manifolds Admitting Certain Critical Metric

In the present paper, we introduce the notion of $\ast$-Miao-Tam critical equation on almost contact metric manifolds and studied on a class of almost Kenmotsu manifold. It is shown that if the metric of a $(2n + 1)$-dimensional $(k,μ)'$-almost Kenmotsu manifold $(M,g)$ satisfies the $\ast$-Miao-Tam critical equation, then the manifold $(M,g)$ is $\ast$-Ricci flat and locally isometric to the Riemannian product of a $(n + 1)$-dimensional manifold of constant sectional curvature $-4$ and a flat $n$-dimensional manifold. Finally, an illustrative example is presented to support the main theorem.

Noncompactness and maximum mobility of type III Ricci-flat self-dual neutral Walker four-manifolds

It is shown that a self-dual neutral Einstein four-manifold of Petrov type III, admitting a two-dimensional null parallel distribution compatible with the orientation, cannot be compact or locally homogeneous, and its maximum possible degree of mobility is 3. Diaz-Ramos, Garcia-Rio and Vazquez-Lorenzo found a general coordinate form of such manifolds. The present paper also provides a modified version of that coordinate form, valid in a suitably defined generic case and, in a sense, "more canonical" than the usual formulation. Moreover, the local-isometry types of manifolds as above having the…

$N(k)$-contact metric as $\ast$-conformal Ricci soliton

The aim of this paper is characterize a class of contact metric manifolds admitting $\ast$-conformal Ricci soliton. It is shown that if a $(2n + 1)$-dimensional $N(k)$-contact metric manifold $M$ admits $\ast$-conformal Ricci soliton or $\ast$-conformal gradient Ricci soliton, then the manifold M is $\ast$-Ricci at and locally isometric to the Riemannian of a flat $(n + 1)$-dimensional manifold and an $n$-dimensional manifold of constant curvature 4 for $n > 1$ and flat for $n = 1$. Further, for the first case, the soliton vector field is conformal and for the $\ast$-gradient case, the potenti…

具有对称性的Bismut Ricci平坦流形

Bismut Ricci flat manifolds with symmetries

本文构造了具有不变Bismut Ricci平坦联络的紧齐性黎曼流形例子，证明广义Alekseevsky-Kimelfeld定理不成立，并给出5维分类及稳定性讨论。

具有Kähler和Ricci孤立子结构的Clairaut反不变黎曼映射

Clairaut anti-invariant Riemannian maps with Kähler and Ricci soliton structures

本文研究带Ricci孤立子的Kähler流形间的Clairaut反不变黎曼映射，推导曲率关系、各类几何结构条件及曲率与李导数的关系，并给出非平凡实例。

Kinematic Description of Ricci Solitons in Fluid Spacetimes

We consider the kinematics of specific fluid spacetimes admitting timelike congruences of Ricci Solitons. These fluids includes string cloud, string fluid, perfect fluid, radially symmetric fluid, anisotropic fluid and relativistic magneto-fluid. Results are obtained and important physical aspects are discussed.

仿切触几何中的 h-几乎 Ricci-Yamabe 孤立子

H-almost Ricci-Yamabe solitons in paracontact geometry

本文在仿切触几何框架下分类了 h-几乎 Ricci-Yamabe 孤立子，系统刻画了 para-Kenmotsu、para-Sasakian 和 para-cosymplectic 流形上的相关结构，并给出两个实例加以说明。

The Alekseevskii Conjecture in 9 and 10 dimensions

We show that noncompact homogeneous spaces not diffeomorphic to Euclidean space of dimension 9 or 10 admit no homogeneous Einstein metrics of negative Ricci curvature, with only three potential exceptions. The main ingredient in the proof is to show, via a cohomogeneity-one approach, that noncompact homogeneous spaces admitting an ideal isomorphic to $ \mathfrak{sl}_2(\mathbb{R}) $ admit no homogeneous Einstein metrics of negative Ricci curvature.

Geometry of para-Sasakian metric as an almost conformal $η$-Ricci soliton

In this paper, we initiate the study of conformal $η$-Ricci soliton and almost conformal $η$-Ricci soliton within the framework of para-Sasakian manifold. We prove that if para-Sasakian metric admits conformal $η$-Ricci soliton, then the manifold is $η$-Einstein and either the soliton vector field $V$ is Killing or it leaves $ϕ$ invariant. Here, we have shown the characteristics of the soliton vector field $V$ and scalar curvature when the manifold admitting conformal $η$-Ricci soliton and vector field is pointwise collinear with the characteristic vector field $ξ$. Next, we show that a para-S…

$(\u03b5)$-殆仿切触度量流形中的$\u03b7$-Ricci孤立子

$η$-Ricci solitons in $(\varepsilon)$-almost paracontact metric manifolds

该文针对$(\u03b5)$-殆仿切触度量流形，研究了两类势向量场情形下的$\u03b7$-Ricci孤立子，分析了相关特殊流形的孤立子容许性，并结合平行对称(0,2)张量场得到了若干研究结果。

具有常长度势场的有限体积非紧Ricci孤子

Non-compact Ricci Solitons of Finite Volume with Potential Field of Constant Length

研究具有常长度势场的有限体积非紧Ricci孤子，在特定假设下证明其平凡性，作为应用得到相关Ricci孤子的刚性和不存在性结果，在三维中有进一步推导及与相关分类比较，还给出例子和反例说明假设必要性。

On the fundamental group of non-collapsed ancient Ricci flows

We show that any manifold admitting a non-collapsed, ancient Ricci flow must have finite fundamental group. This generalizes what was known for $κ$-solutions in dimensions 2, 3. We furthermore show that this fundamental group must be a quotient of the fundamental group of the regular part of any tangent flow at infinity.

$\ast$-Ricci-Yamabe Soliton and Contact Geometry

It is well known that a unit sphere admits Sasakian 3-structure. Also, Sasakian manifolds are locally isometric to a unit sphere under several curvature and critical conditions. So, a natural question is: Does there exist any curvature or critical condition under which a Sasakian 3-manifold represents a geometrical object other than the unit sphere? In this regard, as an extension of the $\ast$-Ricci soliton, the notion of $\ast$-Ricci-Yamabe soliton is introduced and studied on two classes contact metric manifolds. A $(2n + 1)$-dimensional non-Sasakian $N(k)$-contact metric manifold admitting…

On the collapsing rate of the Kähler-Ricci flow with finite-time singularity

This short note studies the collapsing behavior of the Kähler-Ricci flow on a compact Kähler manifold X admitting a holomorphic submersion X -> B where B is a Kähler manifold of lower dimension than X. We give cohomological and curvature conditions under which the fibers collapse at the optimal rate ~(T-t)^{1/2}

Non-solvable Lie groups with negative Ricci curvature

Until a couple of years ago, the only known examples of Lie groups admitting left-invariant metrics with negative Ricci curvature were either solvable or semisimple. We use a general construction from a previous article of the second named author to produce a great amount of examples with compact Levy factor. Given a compact semisimple real Lie algebra $\mathfrak u$ and a real representation $π$ satisfying some technical properties, the construction returns a metric Lie algebra $\mathfrak l(\mathfrak u,π)$ with negative Ricci operator. In this paper, when $\mathfrak u$ is assumed to be simple,…

通过 $\ast-\boldsymbol{\kappa}$-Ricci-Bourguignon 几乎孤子看 Kenmotsu 接触几何

Kenmotsu Contact Geometry Through the Lens of $\ast-\boldsymbolκ$-Ricci-Bourguignon Almost Solitons

研究 Kenmotsu 流形上 $\ast-\boldsymbol{\kappa}$-Ricci-Bourguignon 几乎孤子的性质，推导标量曲率，构造向量场，并探索扭形向量场的应用，给出五维实例。

K-Stability for Fano Manifolds with Torus Action of Complexity One

We consider Fano manifolds admitting an algebraic torus action with general orbit of codimension one. Using a recent result of Datar and Szekelyhidi, we effectively determine the existence of Kahler-Ricci solitons for those manifolds via the notion of equivariant K-stability. This allows us to give new examples of Kahler-Einstein Fano threefolds, and Fano threefolds admitting a non-trivial Kahler-Ricci soliton.

Towards a Classification of pseudo-Riemannian Geometries Admitting Twistor Spinors

We show that given a conformal structure whose holonomy representation fixes a totally lightlike subspace of arbitrary dimension, there is always a local metric in the conformal class off a singular set which is Ricci-isotropic and gives rise to a parallel, totally lightlike distribution on the tangent bundle. This naturally applies to parallel spin tractors resp. twistor spinors on conformal spin manifolds and clarifies which twistor spinors are locally equivalent to parallel spinors. Moreover, we study the zero set of a twistor spinor using the curved orbit decomposition for parabolic geomet…

Complete Ricci-flat metrics through a rescaled exhaustion

Typical existence result on Ricci-flat metrics is in manifolds of finite geometry, that is, on $F=\bar F-D$ where $\bar F$ is a compact Kähler manifold and $D$ is a smooth divisor. We view this existence problem from a different perspective. For a given complex manifold $X$, we take a suitable exhaustion $\{X_r\}_{r>0}$ admitting complete \ke s of negative Ricci. Taking a positive decreasing sequence $\{λ_r\}_{r>0}, \lim_{r\to\infty}λ_r=0$, we rescale the metric so that $g_r$ is the complete \ke\ in $X_r$ of Ricci curvature $-λ_r$. The idea is to show the limiting metric $\lim_{r\to\infty} g_r…

非负 Ricci 曲率与维数小于 12 时的虚拟交换性

Nonnegative Ricci curvature and virtual abelianness in dimensions less than 12

对于非负Ricci曲率且直径次线性增长的流形，若基本群含无挠幂零子群，则维数需满足下界；特别地，维数小于12时基本群几乎交换，证明基于RCD空间维数估计。

五维 Ricci 正曲率度量的模空间

Moduli spaces of Ricci positive metrics in dimension five

本文利用 spin$^c$ Dirac 算子的 $\eta$ 不变量区分正 Ricci 曲率度量模空间的连通分支，并构造无穷多个五维主 $S^1$ 丛流形使其模空间各有无穷多分支。

Multiplier Hermitian-Einstein metrics on Fano manifolds of KSM-type

In this article we focus on multiplier Hermitian-Einstein metrics introduced by Mabuchi which include Kähler-Einstein metrics, Kähler-Ricci solitons and Mabuchi solitons as special cases. We also focus on KSM-manifolds, which are introduced by the first author as toric bundles, to establish a criterion for the existence of multiplier Hermitian-Einstein metrics in terms of KSM-data. An explicit example for a KSM-manifold admitting a family of multiplier Hermitian-Einstein metrics is constructed by using a continuous path connecting a Kähler-Ricci soliton and a Mabuchi soliton.

Invariant pseudo Kaehler metrics in dimension four

Four dimensional simply connected Lie groups admitting a pseudo Kähler metric are determined. The corresponding Lie algebras are modelized and the compatible pairs $(J,ω)$ are parametrized up to complex isomorphism (where $J$ is a complex structure and $ω$ is a symplectic structure). Such structure gives rise to a pseudo Riemannian metric $g$ for which $J$ is parallel. It is proved that most of these complex homogeneous spaces admit a pseudo Kähler Einstein metric. Ricci flat and flat metrics are determined. In particular Ricci flat unimodular Kähler Lie algebras are flat in dimension four. Ot…

正中间Ricci曲率在连通和上的研究

Positive intermediate Ricci curvature on connected sums

研究正$k^{th}$中间Ricci曲率下连通和的构造问题，提出$k$-核度量概念并证明线性球丛连通和在特定$k$值范围内允许该曲率，同时给出$\mathbb{H} P^n$和$\mathbb{O}P^2$的最优核度量实例。

具有余二维环面作用的单连通流形上的正里奇曲率

Positive Ricci curvature on simply-connected manifolds with cohomogeneity-two torus actions

本文针对余二维环面作用的闭单连通流形，通过替代证明，在无限子族上构造了正里奇曲率度量，并推广到所有允许该作用的5维和6维流形。

H-projectively-equivalent four-dimensional Kahler manifolds

The paper is devoted to the investigation of four-dimensional Kahler manifolds admitting non-affine H-projective mappings. We find all such manifolds which are non-Einstein. In the paper also Kahler manifolds admitting infinitesimal H-projective transformations are determined. It is proved that the class of Kahler manifolds admitting H-projective mappings includes generalized equidistant Kahler manifolds. The explicit expression for the metrics of Ricci-flat four-dimensional generalized equidistant manifolds is given.

里齐曲率与具有大贝蒤数的极小超曲面

Ricci curvature and minimal hypersurfaces with large Betti numbers

研究构造了高维里齐曲率正的闭合流形，其嵌入的双侧极小超曲面具有Morse指数为一且贝蒤数不一致有界的特性。

Einstein-Weyl structures on almost cosymplectic manifolds

In this article, we study Einstein-Weyl structures on almost cosymplectic manifolds. First we prove that an almost cosymplectic $(κ,μ)$-manifold is Einstein or cosymplectic if it admits a closed Einstein-Weyl structure or two Einstein-Weyl structures. Next for a three dimensional compact almost $α$-cosymplectic manifold admitting closed Einstein-Weyl structures, we prove that it is Ricc-flat. Further, we show that an almost $α$-cosymplectic admitting two Einstein-Weyl structures is either Einstein or $α$-cosymplectic, provided that its Ricci tensor is commuting. Finally, we prove that a compac…