Compactness of solutions to the Yamabe problem. II

A compactness theorem of the fractional Yamabe problem, Part I: The non-umbilic conformal infinity

Assume that $(X, g^+)$ is an asymptotically hyperbolic manifold, $(M, [\bar{h}])$ is its conformal infinity, $ρ$ is the geodesic boundary defining function associated to $\bar{h}$ and $\bar{g} = ρ^2 g^+$. For any $γ\in (0,1)$, we prove that the solution set of the $γ$-Yamabe problem on $M$ is compact in $C^2(M)$ provided that convergence of the scalar curvature $R[g^+]$ of $(X, g^+)$ to $-n(n+1)$ is sufficiently fast as $ρ$ tends to 0 and the second fundamental form on $M$ never vanishes. Since most of the arguments in blow-up analysis performed here is irrelevant to the geometric assumption i…

Compactness results for linearly perturbed Yamabe problem on manifolds with boundary

Let M,g a compact Riemannian n-dimensional manifold. It is well know that, under certain hypothesis, in the conformal class of g there are scalar-flat metrics that have the boundary of M as a constant mean curvature hypersurface. Also, under certain hypothesis, it is known that these metrics are a compact set. In this paper we prove that, both in the case of umbilic and non-umbilic boundary, if we linearly perturb the mean curvature term with a negative smooth function, the set of solutions of Yamabe problem is still a compact set.

A non-compactness result on the fractional Yamabe problem in large dimensions

Let $(X^{n+1}, g^+)$ be an $(n+1)$-dimensional asymptotically hyperbolic manifold with a conformal infinity $(M^n, [\hat{h}])$. The fractional Yamabe problem addresses to solve \[P^γ[g^+,\hat{h}] (u) = cu^{n+2γ\over n-2γ}, \quad u > 0 \quad \text{on } M\] where $c \in \mathbb{R}$ and $P^γ[g^+,\hat{h}]$ is the fractional conformal Laplacian whose principal symbol is $(-Δ)^γ$. In this paper, we construct a metric on the half space $X = \mathbb{R}^{n+1}_+$, which is conformally equivalent to the unit ball, for which the solution set of the fractional Yamabe equation is non-compact provided that $…

Response to a question of Yanyan Li and Luc Nguyen in their paper "A compactness theorem for a fully nonlinear Yamabe problem under a lower Ricci curvature bound", arXiv:1212.0460

This paper has been withdrawn, see the replacement arXiv:1302.6670.

三维CR Yamabe问题的紧性结果

A compactness result for the CR Yamabe problem in three dimensions

本文通过blow-up分析证明了三维紧致严格伪凸CR流形上CR Yamabe问题解集的紧性，并得出不CR等价于$S^3$的CR-可嵌入流形紧性成立的推论。

边界 Yamabe 问题中紧致性的临界维数，II

On Critical Dimensions for Compactness in the Boundary Yamabe Problem, II

本文确定了边界 Yamabe 问题中紧致性的临界维数，给出不同边界条件下的尖锐范围，并通过标量修正与几何公式证明过渡维数。

On the conformal scalar curvature equation and related problems

We review recent compactness and non-compactness results for the Yamabe equation. We also discuss the asymptotic behavior of the parabolic Yamabe flow.

A fully nonlinear version of the Yamabe problem on locally conformally flat manifolds with umbilic boundary

In this paper we establish existence and compactness of solutions to a general fully nonlinear version of the Yamabe problem on locally conformally flat Riemannian manifolds with umbilic boundary.

On perturbations of the fractional Yamabe problem

The fractional Yamabe problem, proposed by González-Qing (2013, Anal. PDE) is a geometric question which concerns the existence of metrics with constant fractional scalar curvature. It extends the phenomena which were discovered in the classical Yamabe problem and the boundary Yamabe problem to the realm of nonlocal conformally invariant operators. We investigate a non-compactness property of the fractional Yamabe problem by constructing bubbling solutions to its small perturbations.

正Yamabe--Escobar问题带极小边界的紧致性与非紧致性

Compactness and Noncompactness for the Positive Yamabe--Escobar Problem with Minimal Boundary

本文证明正Yamabe--Escobar问题在3≤n≤14时紧致性猜想成立，并构造n≥15的非紧致序列，确定各维度阈值，同时验证Weyl--脐性消失猜想并给出反例。

五维紧性与等价非紧性对于CR Yamabe问题

Compactness in Dimension Five and Equivariant Noncompactness for the CR Yamabe Problem

本文研究了五维CR Yamabe方程的紧性和非紧性现象，通过建立先验估计和构造非标准CR结构，证明了在等价设定下的非紧性。

Yamabe稳定性优化元的存在性

Existence of Yamabe stability optimizers

该研究证明了满足特定阈值条件的高维正Yamabe不变量闭Riemann流形上Yamabe不等式稳定性优化元的存在性，明确了不同情形下的紧性阈值与严格不等式成立的条件。

Blow-up phenomena for the Yamabe equation

Let (M,g) be a compact Riemannian manifold of dimension n \geq 3. The Compactness Conjecture asserts that the set of constant scalar curvature metrics in the conformal class of g is compact unless (M,g) is conformally equivalent to the round sphere. In this paper, we construct counterexamples to this conjecture in dimensions n \geq 52.

边界 Yamabe 问题中紧致性的临界维数，I

On critical dimensions for compactness in the boundary Yamabe problem, I

本文构造了边界 Yamabe 方程具有无界正解序列的光滑非局部共形平坦度量，确定了不同曲率条件下紧致性失效的临界维数范围，并证明了约化能量二次项具有负的非退化局部极值。

Yamabe问题的变分方法：紧Riemann流形上的共形变换与标量曲率

A Variational Approach to the Yamabe Problem: Conformal Transformations and Scalar Curvature on Compact Riemannian Manifolds

本文用变分与集中紧性方法研究紧Riemann流形上的Yamabe问题，证明在$\lambda(M)<\lambda(S^n)$条件下存在共形常标量曲率度量。

Volume comparison and the sigma_k-Yamabe problem

In this paper we study the problem of finding a conformal metric with the property that the k-th elementary symmetric polynomial of the eigenvalues of its Weyl-Schouten tensor is constant. A new conformal invariant involving maximal volumes is defined, and this invariant is then used in several cases to prove existence of a solution, and compactness of the space of solutions (provided the conformal class admits an admissible metric). In particular, the problem is completely solved in dimension four, and in dimension three if the manifold is not simply connected.

A compactness theorem for scalar-flat metrics on 3-manifolds with boundary

Let (M,g) be a compact Riemannian three-dimensional manifold with boundary. We prove the compactness of the set of scalar-flat metrics which are in the conformal class of g and have the boundary as a constant mean curvature hypersurface. This involves a blow-up analysis of a Yamabe-type equation with critical Sobolev exponent on the boundary.

三维中具有常数量曲率和常边界平均曲率的共形度量的紧致性定理

A compactness theorem for conformal metrics with constant scalar curvature and constant boundary mean curvature in dimension three

该研究证明了三维带边界紧致流形上具有正常数量曲率和常边界平均曲率的共形度量集合的紧致性，通过Yamabe方程的爆破分析实现。

The effect of linear perturbations on the Yamabe problem

In conformal geometry, the Compactness Conjecture asserts that the set of Yamabe metrics on a smooth, compact, aspherical Riemannian manifold (M,g) is compact. Established in the locally conformally flat case by Schoen [43,44] and for n\leq 24 by Khuri-Marques-Schoen [26], it has revealed to be generally false for n\geq 25 as shown by Brendle [8] and Brendle-Marques [9]. A stronger version of it, the compactness under perturbations of the Yamabe equation, is addressed here with respect to the linear geometric potential n-2/4(n-1) Scal_g, Scal_g being the Scalar curvature of (M,g). We show that…

对偶Yamabe流及相关积分流

A dual Yamabe flow and related integral flows

研究黎曼流上涉及Riesz势的非线性积分流，通过引入对偶Q曲率分析HLS临界区域的集中紧性现象，并在积分核匹配Green函数时将其视为对偶Yamabe流，证明了其在单位球及局部共形平坦流形上的收敛性。

Fractional conformal Laplacians and fractional Yamabe problems

Based on the relations between scattering operators of asymptotically hyperbolic metrics and Dirichlet-to-Neumann operators of uniformly degenerate elliptic boundary value problems, we formulate fractional Yamabe problems that include the boundary Yamabe problem studied by Escobar. We observe an interesting Hopf type maximum principle together with interplays between analysis of weighted trace Sobolev inequalities and conformal structure of the underlying manifolds, which extend the phenomena displayed in the classic Yamabe problem and boundary Yamabe problem.

On a fully nonlinear Yamabe problem

We solve the $σ_2$-Yamabe problem for a non locally conformally flat manifold of dimension $n>8$.

球冠上Yamabe问题的变号解

Sign-changing solutions to the Yamabe problem on a spherical cap

研究球冠上Yamabe问题，利用对称性和紧性损失分析，证明了当球冠包含于标准n-球面的半球且n=5或n≥7时，存在无穷多个变号解。

Compactness of scalar-flat conformal metrics on low-dimensional manifolds with constant mean curvature on boundary

We concern $C^2$-compactness of the solution set of the boundary Yamabe problem on smooth compact Riemannian manifolds with boundary provided that their dimensions are $4$, $5$ or $6$. By conducting a quantitative analysis of a linear equation associated with the problem, we prove that the trace-free second fundamental form must vanish at possible blow-up points of a sequence of blowing-up solutions. Applying this result and the positive mass theorem, we deduce the $C^2$-compactness for all $4$-manifolds (which may be non-umbilic). For the $5$-dimensional case, we also establish that a sum of …

Estimates and Existence Results for a Fully Nonlinear Yamabe Problem on Manifolds with Boundary

This paper concerns a fully nonlinear version of the Yamabe problem on manifolds with boundary. We establish some existence results and estimates of solutions.

A fully nonlinear version of the Yamabe problem and a Harnack type inequality

We present some results on a fully nonlinear version of the Yamabe problem and a Harnack type inequality for general conformally invariant fully nonlinear second order elliptic equations.

On some conformally invariant fully nonlinear equations, Part II: Liouville, Harnack and Yamabe

The Yamabe problem concerns finding a conformal metric on a given closed Riemannian manifold so that it has constant scalar curvature. This paper concerns mainly a fully nonlinear version of the Yamabe problem and the corresponding Liouville type problem.

The Yamabe problem on Dirichlet spaces

We continue our previous work studying critical exponent semilinear elliptic (and subelliptic) problems which generalize the classical Yamabe problem. In [3] the focus was on metric-measure spaces with an `almost smooth' structure, with stratified spaces furnishing the key examples. The criterion for solvability there is phrased in terms of a strict inequality of the global Yamabe invariant with a `local Yamabe invariant', which captures information about the local singular structure. All of this is generalized here to the setting of Dirichlet spaces which admit a Sobolev inequality and satisf…

Blow-up phenomena for linearly perturbed Yamabe problem on manifolds with umbilic boundary

We build blowing-up solutions for linear perturbation of the Yamabe problem on manifolds with umbilic boundary, provided the Weyl tensor is nonzero everywhere on the boundary and the dimension of the manifold is n>10.

Linear perturbation of the Yamabe problem on manifolds with boundary

We build blowing-up solutions for linear perturbation of the Yamabe problem on manifolds with boundary, provided the dimension of the manifold is n>6 and the trace-free part of the second fundamental form is non-zero everywhere on the boundary.

A priori estimates for the Yamabe problem in the non-locally conformally flat case

Given a compact Riemannian manifold, with positive Yamabe quotient, not conformally diffeomorphic to the standard sphere, we prove a priori estimates for solutions to the Yamabe problem. We restrict ourselves to the dimensions less than or equal to 7, where the Positive Mass Theorem is known to be true. We also show that, when the dimension is greater than or equal to 6, the Weyl tensor has to vanish at a point where solutions to the Yamabe equation blow up.

Blowing up solutions for supercritical Yamabe problems on manifolds with umbilic boundary

We build blowing-up solutions for a supercritical perturbation of the Yamabe problem on manifolds with umbilic boundary provided the dimension of the manifold is n>7 and that the Weyl tensor W(x) is not vanishing on the boundary of M.

CR 雅可比方程奇异解的渐近方法

Asymptotic approach to singular solutions for the CR Yamabe equation

研究海森堡群中福兰德 - 斯坦 - 索伯列夫嵌入次临界逼近最优函数紧致性损失，防边界爆破时中心对称最大化器集中于中心，获远离极点爆破率与渐近轮廓，建立近临界索伯列夫问题对应渐近。

Yamabe类型问题的变号解

Sign-changing solutions for a Yamabe type problem

本文研究了Yamabe类型问题中变号解的存在性，通过几何条件确保了临界椭圆方程解的存在。

A Yamabe-type problem on smooth metric measure spaces

We describe and partially solve a natural Yamabe-type problem on smooth metric measure spaces which interpolates between the Yamabe problem and the problem of finding minimizers for Perelman's $ν$-entropy. This problem reduces in all dimensions on Euclidean space to the characterization of the minimizers of the family of Gagliardo--Nirenberg--Sobolev inequalities studied by Del Pino and Dolbeault. We show that minimizers always exist on a compact manifold provided the so-called weighted Yamabe constant is strictly less than its value on Euclidean space. We also show that strict inequality hold…

On some conformally invariant fully nonlinear equations

We will report some results concerning the Yamabe problem and the Nirenberg problem. Related topics will also be discussed. Such studies have led to new results on some conformally invariant fully nonlinear equations arising from geometry. We will also present these results which include some Liouville type theorems, Harnack type inequalities, existence and compactness of solutions to some nonlinear version of the Yamabe problem.

A conformal Yamabe problem with potential on the euclidean space

We consider, in the Euclidean setting, a conformal Yamabe-type equation related to a potential generalization of the classical constant scalar curvature problem and which naturally arises in the study of Ricci solitons structures. We prove existence and nonexistence results, focusing on the radial case, under some general hypothesis on the potential.

A formal Riemannian structure on conformal classes and uniqueness for the $σ_{2}$-Yamabe problem

We define a new formal Riemannian metric on a conformal classes of four-manifolds in the context of the $σ_2$-Yamabe problem. Exploiting this new variational structure we show that solutions are unique unless the manifold is conformally equivalent to the round sphere.

非紧流形上的完全非线性Yamabe型问题

Fully nonlinear Yamabe-type problems on non-compact manifolds

本文研究非紧流形上的完全非线性Yamabe型问题，在正、负两种情形下证明了存在性结果，并构造了满足定理假设的扭曲积端和渐近平坦端流形的显式例子。

Blowing up solutions for supercritical Yamabe problems on manifolds with non umbilic boundary

We build blowing-up solutions for a supercritical perturbation of the Yamabe problem on manifolds with boundary, provided the dimension of the manifold is n>6 and the trace-free part of the second fundamental form is non-zero everywhere on the boundary.

Compactness of conformal metrics with constant $Q$-curvature. I

We study compactness for nonnegative solutions of the fourth order constant $Q$-curvature equations on smooth compact Riemannian manifolds of dimension $\ge 5$. If the $Q$-curvature equals $-1$, we prove that all solutions are universally bounded. If the $Q$-curvature is $1$, assuming that Paneitz operator's kernel is trivial and its Green function is positive, we establish universal energy bounds on manifolds which are either locally conformally flat (LCF) or of dimension $\le 9$. Moreover, assuming in addition that a positive mass type theorem holds for the Paneitz operator, we prove compact…

The Yamabe problem on stratified spaces

We introduce new invariants of a Riemannian singular space, the local Yamabe and Sobolev constants, and then go on to prove a general version of the Yamabe theorem under that the global Yamabe invariant of the space is strictly less than one or the other of these local invariants. This rests on a small number of structural assumptions about the space and of the behavior of the scalar curvature function on its smooth locus. The second half of this paper shows how this result applies in the category of smoothly stratified pseudomanifolds, and we also prove sharp regularity for the solutions on t…

The Yamabe problem for higher order curvatures

Let M be a compact Riemannian manifold of dimension n. The k-curvature, for k=1,2,..n, is defined as the k-th elementary symmetric polynomial of the eigenvalues of the Schouten tenser. The k-Yamabe problem is to prove the existence of a conformal metric whose k-curvature is a constant. When k=1, it reduces to the well-known Yamabe problem. Under the assumption that the metric is admissible, the existence of solutions to the k-Yamabe problem was recently proved by Gursky and Viaclovsky for k>n/2. In this paper we prove the existence of solutions for the remaining cases k <n/2, k=n/2, assuming t…

Delaunay-type singular solutions for the fractional Yamabe Problem

We construct Delaunay-type solutions for the fractional Yamabe problem with an isolated singularity $(-Δ)^γw = c_{n, γ} w^{\frac{n+2γ}{n-2γ}}, w>0 \ \mbox{in} \ \mathbb{R}^n \backslash \{0\}$ We follow a variational approach, in which the key is the computation of the fractional Laplacian in polar coordinates.

Nodal solutions for the fractional Yamabe problem on Heisenberg groups

We prove that the fractional Yamabe equation $\mathcal L_γu=|u|^\frac{4γ}{Q-2γ}u$ on the Heisenberg group $\mathbb H^n$ has $[\frac{n+1}{2}]$ sequences of nodal (sign-changing) weak solutions whose elements have mutually different nodal properties, where $\mathcal L_γ$ denotes the CR fractional sub-Laplacian operator on $\mathbb H^n$, $Q=2n+2$ is the homogeneous dimension of $\mathbb H^n$, and $γ\in \bigcup_{k=1}^n[k,\frac{kQ}{Q-1})$. Our argument is variational, based on a Ding-type conformal pulling-back transformation of the original problem into a problem on the CR sphere $S^{2n+1}$ combin…

Riemannian流形上完全非线性Yamabe问题的边界估计

Boundary estimates for a fully nonlinear Yamabe problem on Riemannian manifolds

本文研究带边Riemannian流形上完全非线性Yamabe方程的Dirichlet边值问题，在假设下解存在的前提下导出先验边界二阶导数估计并证明光滑解的存在性，且该估计对插值方程族保持一致。

Le probléme de Yamabe avec singularités et la conjecture de Hebey-Vaugon

In the first part of this thesis, we study the Yamabe problem with singularities, that we can announce as follow: Given a compact Riemannian manifold $(M,g)$, find a constant scalar curvature metric, conformal to $g$, when $g$ has not necessarily the usual regularity (it can be $C^1$). To solve this problem, we start the study of the Yamabe type equations. We show that all the known properties in the smooth case are still valid. Under some assumptions, we prove the existence and uniqueness of solutions. The second part is dedicated to the Hebey-Vaugon conjecture, stated in their paper about th…

光滑度量测度空间的质量型不变量及其与分数阶Yamabe问题的关系

A mass-type invariant for smooth metric measure spaces and its relation with the fractional Yamabe problem

在渐近Schwarzschild光滑度量测度空间上定义类似ADM质量的不变量，证明其几何不变性，并揭示与分数阶Yamabe问题及Green函数的关系。

The Lichnerowicz and Obata first eigenvalue theorems and the Obata uniqueness result in the Yamabe problem on CR and quaternionic contact manifolds

We report on some aspects and recent progress in certain problems in the sub-Riemannian CR and quaternionic contact (QC) geometries. The focus are the corresponding Yamabe problems on the round spheres, the Lichnerowicz-Obata first eigenvalue estimates, and the relation between these two problems. A motivation from the Riemannian case highlights new and old ideas which are then developed in the settings of Iwasawa sub-Riemannian geometries.

形式自共轭、共形协变、多项微分算子的Yamabe问题

Yamabe problems for formally self-adjoint, conformally covariant, polydifferential operators

本文探讨了形式自共轭、共形协变多项微分算子的Yamabe问题，分析了球面上的唯一性结果及一般情况下的非唯一性，并指出了一些开放性问题，可能为多项微分算子的Yamabe问题提供解决思路。

On the Chern-Yamabe flow

On a closed balanced manifold, we show that if the Chern scalar curvature is small enough in a certain Sobolev norm then a slightly modified version of the Chern-Yamabe flow~\cite{Angella:2015aa} converges to a solution of the Chern-Yamabe problem. We also prove that if the Chern scalar curvature, on closed almost-Hermitian manifolds, is close enough to a constant function in a Hölder norm then the Chern-Yamabe problem has a solution for generic values of the fundamental constant.

Singular Yamabe metrics by equivariant reduction

We construct singular solutions to the Yamabe equation using a reduction of the problem in an equivariant setting. This provides a non-trivial geometric example for which the analysis is simpler than in Mazzeo-Pacard program. Our construction provides also a non-trivial example of a weak solution to the Yamabe problem involving an equation with (smooth) coefficients.

Extremals for the Sobolev inequality on the seven dimensional quaternionic Heisenberg group and the quaternionic contact Yamabe problem

A complete solution to the quaternionic contact Yamabe problem on the seven dimensional sphere is given. Extremals for the Sobolev inequality on the seven dimensional Hesenberg group are explicitly described and the best constant in the $L^2$ Folland-Stein embedding theorem is determined.

The Yamabe flow on asymptotically Euclidean manifolds with nonpositive Yamabe constant

We study the Yamabe flow on asymptotically flat manifolds with non-positive Yamabe constant $Y\leq 0$. Previous work by the second and third named authors \cite{ChenWang} showed that while the Yamabe flow always converges in a global weighted sense when $Y>0$, the flow must diverge when $Y\leq 0$. We show here in the $Y\leq 0$ case however that after suitable rescalings, the Yamabe flow starting from any asymptotically flat manifold must converge to the unique positive function which solves the Yamabe problem on a compactification of the original manifold.