Nicola Fusco, Massimiliano Morini
We settle the case of equality for the relative isoperimetric inequality outside any arbitrary convex set with not empty interior.
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We prove an sharp anisotropic isoperimetric inequality for a domain outside an Euclidean ball in $\mathbb{R}^n$ for $n\geq 2$. The proof applies the ABP method to a Neumann boundary value problem.
Quantitative estimates for the relative isoperimetric problem and its gradient flow outside convex bodies in the plane
本文研究了平面中凸体外的相对等周问题，提出了三个定量结果，包括临界点的刚性估计、梯度流收敛速率以及最小化问题的稳定性，首次采用流方法证明稳定性。
It is known that a simply connected Riemann surface satisfies the isoperimetric equality if and only if it has constant Gaussian curvature. In this article, we show that Randers Poincaré disc satisfies the isoperimetric equality with respect to different volume forms. These metrics do not necessarily have constant (negative) flag curvature. Thus we show that the Osserman's result \cite{RO} in the Riemannian case can not be extended to the corresponding Finslerian case.
The sharp isoperimetric inequality for varifolds in codimension two
本文证明了一类varifolds的Michael-Simon不等式，在余维数2时达到尖锐，并由此得到等号仅在圆盘取得的尖锐等周不等式，证明基于Brendle-Eichmair的最优传输方法。
We study, on a weighted Riemannian manifold of Ric$_{N} \geq K > 0$ for $N < -1$, when equality holds in the isoperimetric inequality. Our main theorem asserts that such a manifold is necessarily isometric to the warped product $\mathbb{R} \times_{\cosh(\sqrt{K/(1-N)}t)} Σ^{n-1}$ of hyperbolic nature, where $Σ^{n-1}$ is an $(n-1)$-dimensional manifold with lower weighted Ricci curvature bound and $\mathbb{R}$ is equipped with a hyperbolic cosine measure. This is a similar phenomenon to the equality condition of Poincaré inequality. Moreover, every isoperimetric minimizer set is isometric to a …
We prove a reverse isoperimetric inequality for domains homeomorphic to a disc with the boundary of curvature bounded below lying in two-dimensional Alexandrov spaces of curvature $\geqslant c$. We also study the equality case.
The Isoperimetric Inequality in Higher-Dimensional Heisenberg Groups
本文证明了高维海森堡群中的锐利水平等周不等式，并刻画了等号成立的条件为Pansu球的左平移和膨胀。
In this note, we consider the isoperimetric inequality on an asymptotically flat manifold with nonnegative scalar curvature, and improve it by using Hawking mass. We also obtain a rigidity result when equality holds for the classical isoperimetric inequality on an asymptotically flat manifold with nonnegative scalar curvature.
In this paper we provide a Bonnesen-style inequality which gives a lower bound for the isoperimetric deficit corresponding to a closed convex curve in terms of some geometrical invariants of this curve. Moreover we give a geometrical interpretation for the case when equality holds.
The Sharp Isoperimetric Inequality in the First Heisenberg Group
本文证明了第一海森堡群中尖锐水平等周不等式，等号条件为Pansu球的左平移和伸缩。
The classical isoperimetric inequality in the Euclidean plane $\mathbb{R}^2$ states that for a simple closed curve $M$ of the length $L_{M}$, enclosing a region of the area $A_{M}$, one gets \begin{align*} L_{M}^2\geqslant 4πA_{M}. \end{align*} In this paper we present the improved isoperimetric inequality, which states that if $M$ is a closed regular simple convex curve, then \begin{align*} L_{M}^2\geqslant 4πA_{M}+8π\left|\widetilde{A}_{E_{\frac{1}{2}}(M)}\right|, \end{align*} where $\widetilde{A}_{E_{\frac{1}{2}}(M)}$ is an oriented area of the Wigner caustic of $M$, and the equality holds …
By using optimal mass transport theory we prove a sharp isoperimetric inequality in ${\sf CD} (0,N)$ metric measure spaces assuming an asymptotic volume growth at infinity. Our result extends recently proven isoperimetric inequalities for normed spaces and Riemannian manifolds to a nonsmooth framework. In the case of $n$-dimensional Riemannian manifolds with nonnegative Ricci curvature, we outline an alternative proof of the rigidity result of S. Brendle (2021). As applications of the isoperimetric inequality, we establish Sobolev and Rayleigh-Faber-Krahn inequalities with explicit sharp const…
Let $(M^n,g)$ be simply connected, complete, with non-positive sectional curvatures, and $Σ$ a 2-dimensional closed integral current (or flat chain mod 2) with compact support in $M$. Let $S$ be an area minimising integral 3-current (resp. flat chain mod 2) such that $\partial S = Σ$. We use a weak mean curvature flow, obtained via elliptic regularisation, starting from $Σ$, to show that S satisfies the optimal Euclidean isoperimetric inequality: $ 6 \sqrtπ\, \mathbf{M}[S] \leq (\mathbf{M}[Σ])^{3/2} $. We also obtain an optimal estimate in case the sectional curvatures of M are bounded from ab…
Affine isoperimetric type inequalities for static convex domains in hyperbolic space
本文提出双曲椭球概念，借助正交投影建立双曲空间中静态凸域的仿射等周型不等式，并刻画等号成立条件。
In this paper, we deals with isoperimetric-type inequalities for closed convex curves in the Euclidean plane R^2. We derive a family of parametric inequalities involving the following geometric functionals associated to a given convex curve with a simple Fourier series proof: length, area of the region included by the curve, area of the domain enclosed by the locus of curvature centers and integral of the radius of curvature. By using our isoperimetric-type inequalities, we also obtain some new geometric Bonnesen-type inequalities. Furthermore we investigate stability properties of such inequa…
Higher order isoperimetric inequalities and rigidity for surfaces in $\R^n$
该研究针对任意余维数欧氏空间的光滑紧致曲面建立高阶等周型不等式，刻画等号情形的刚性结构，推广了已有经典结果，还构造了无法分解为正交圆形模式的三阶等号曲线。
In this paper the author studies the isoperimetric problem in $\re^n$ with perimeter density $|x|^p$ and volume density $1.$ We settle completely the case $n=2,$ completing a previous work by the author: we characterize the case of equality if $0\leq p\leq 1$ and deal with the case $-\infty<p<-1$ (with the additional assumption $0\inΩ$). In the case $n\geq 3$ we deal mainly with the case $-\infty<p<0,$ showing among others that the results in $2$ dimensions do not generalize for the range $-n+1<p<0.$
Isoperimetric and Michael-Simon inequalities on manifolds with asymptotically nonnegative curvature
该研究在渐近非负曲率流形上证明等周不等式成立，在紧集外非负曲率流形上推导Michael-Simon不等式，采用ABP方法并结合几何与谱性质完成证明，拓展了相关不等式的适用条件。
Weighted volume monotonicity and isoperimetric comparison under a lower Ricci curvature bound
本文在Ricci曲率下有界的完备黎曼流形上，建立了加权Bishop-Gromov体积比较定理，证明了在权函数比非递减时加权体积比的单调性，并应用于推导加权等周不等式。
The purpose of this paper is to analyze the isoperimetric inequality for symmetric log-convex probability measures on the line. Using geometric arguments we first re-prove that extremal sets in the isoperimetric inequality are intervals or complement of intervals (a result due to Bobkov and Houdré). Then we give a quantitative form of the isoperimetric inequality, leading to a somehow anomalous behavior. Indeed, it could be that a set is very close to be optimal, in the sense that the isoperimetric inequality is almost an equality, but at the same time is very far (in the sense of the symmetri…
On the Isoperimetric Riemannian Penrose Inequality
本文在最优衰减假设下证明了渐近平坦3-流形上的黎曼彭罗斯不等式，建立了ADM质量与Huisken等周质量的等式，并将结果推广到不要求渐近平坦性的流形上。
We prove that if $(X,\mathsf{d},\mathfrak{m})$ is a metric measure space with $\mathfrak{m}(X)=1$ having (in a synthetic sense) Ricci curvature bounded from below by $K>0$ and dimension bounded above by $N\in [1,\infty)$, then the classic Lévy-Gromov isoperimetric inequality (together with the recent sharpening counterparts proved in the smooth setting by E. Milman for any $K\in \mathbb{R}$, $N\geq 1$ and upper diameter bounds) hold, i.e. the isoperimetric profile function of $(X,\mathsf{d},\mathfrak{m})$ is bounded from below by the isoperimetric profile of the model space. Moreover, if equal…
In this paper, we prove a class of weighted isoperimetric inequalities for bounded domains in hyperbolic space by using the isoperimetric inequality with log-convex density in Euclidean space. As a consequence, we remove the horo-convex assumption of domains in a weighted isoperimetric inequality proved by Scheuer-Xia. Furthermore, we prove weighted isoperimetric inequalities for star-shaped domains in warped product manifolds. Particularly, we obtain a weighted isoperimetric inequality for star-shaped hypersurfaces lying outside a certain radial coordinate slice in the anti-de Sitter-Schwarzs…
Let $D$ be a closed disk centered at the origin in the horizontal hyperplane $\{t=0\}$ of the sub-Riemannian Heisenberg group $\hh^n$, and $C$ the vertical cylinder over $D$. We prove that any finite perimeter set $E$ such that $D\subset E\subset C$ has perimeter larger than or equal to the one of the rotationally symmetric sphere with constant mean curvature of the same volume, and that equality holds only for the spheres using a recent result by Monti and Vittone [12].
Sharp dynamical isoperimetric principle for mean curvature flow
本文为弱平均曲率流建立了尖锐动力等周原理，证明在初始面积固定的流中标准收缩球面唯一最大化消亡时间，并给出最优消亡时间估计及抛物测度等周不等式。
Generalized minimizers for the capillarity energy outside convex obstacles
针对凸障碍物外毛细性能量可能不存在体积约束极小元的问题，通过凸障碍物Hausdorff收敛下的能量收敛结果，证明存在广义极小元，描述其渐近行为并应用于研究等周轮廓与障碍物渐近几何的影响。
New Reverse Isoperimetric Inequalities
本文研究严格凸曲线和曲面的反等周不等式，推导了三个新不等式，并探讨了其几何意义与应用。
Equality in the logarithmic Sobolev inequality
本文研究正 $\mathrm{Ric}_{\infty}$ 加权 Riemann 流形上对数 Sobolev 不等式的等号刚性，借助 Klartag 的针状分解证明等号时必分裂出一维 Gaussian 空间，并给出相关开放问题。
Coordinate isoperimetric mass and a positive mass theorem for distributional scalar curvature
本文通过建立连续渐近平坦度量的坐标等周质量的新渐近表达式，证明了在弱正则性和非负分布标量曲率条件下，该质量具有坐标不变性并满足正质量定理，无需额外拓扑假设。
Let $g=(g_{ij})$ be a complete Riemmanian metric on $\R^2$ with finite total area and $I_g=\inf_γI(γ)$ with $I(γ)=L(γ)(A_{in}(γ)^{-1}+A_{out}(γ)^{-1})$ where $γ$ is any closed simple curve in $\R^2$, $L(γ)$ is the length of $γ$, $A_{in}(γ)$ and $A_{out}(γ)$ are the area of the regions inside and outside $γ$ respectively, with respect to the metric $g$. We prove the existence of a minimizer for $I_g$. As a corollary we obtain a new proof for the existence of a minimizer for $I_{g(t)}$ for any $0<t<T$ when the metric $g(t)=g_{ij}(\cdot,t)=uδ_{ij}$ is the maximal solution of the Ricci flow equati…
We prove certain optimal systolic inequalities for a closed Riemannian manifold (X,g), depending on a pair of parameters, n and b. Here n is the dimension of X, while b is its first Betti number. The proof of the inequalities involves constructing Abel-Jacobi maps from X to its Jacobi torus T^b, which are area-decreasing (on b-dimensional areas), with respect to suitable norms. These norms are the stable norm of g, the conformally invariant norm, as well as other L^p-norms. The case of equality is characterized in terms of the criticality of the lattice of deck transformations of T^b, while th…
We affirmatively solve the analogue of Lord Rayleigh's conjecture on Riemannian manifolds with positive Ricci curvature for any clamped plates in 2 and 3 dimensions, and for sufficiently large clamped plates in dimensions beyond 3. These results complement those from the flat (M. Ashbaugh & R. Benguria, 1995, and N. Nadirashvili, 1995) and negatively curved (A. Kristály, 2020) cases that are valid only in 2 and 3 dimensions, and at the same time also provide the first positive answer to Lord Rayleigh's conjecture in higher dimensions. The proofs rely on an Ashbaugh-Benguria-Nadirashvili-Talent…
We obtain a sharp characterization of the Euclidean ball among all convex bodies K whose boundary has a pointwise k-th mean curvature not smaller than a geometric constant at almost all normal points. This geometric constant depends only on the volume and the boundary area of K. We deduce this characterization from a new isoperimetric-type inequality for arbitrary convex bodies, for which the equality is achieved uniquely by balls. This second result is proved in a more general context of generalized mean-convex sets. Finally we positively answer a question left open in [FLW19] proving a furth…
In this paper we consider complete noncompact Riemannian manifolds $(M, g)$ with nonnegative Ricci curvature and Euclidean volume growth, of dimension $n \geq 3$. We prove a sharp Willmore-type inequality for closed hypersurfaces $\partial Ω$ in $M$, with equality holding true if and only if $(M{\setminus}Ω, g)$ is isometric to a truncated cone over $\partialΩ$. An optimal version of Huisken's Isoperimetric Inequality for $3$-manifolds is obtained using this result. Finally, exploiting a natural extension of our techniques to the case of parabolic manifolds, we also deduce an enhanced version …
The Positive Mass Conjecture states that any complete asymptotically flat manifold of nonnnegative scalar curvature has nonnegative mass. Moreover, the equality case of the Positive Mass Conjecture states that in the above situation, if the mass is zero, then the Riemannian manifold must be Euclidean space. The Positive Mass Conjecture was proved by R. Schoen and S.-T. Yau for all manifolds of dimension less than 8, and it was proved by E. Witten for all spin manifolds. In this paper, we consider complete asymptotically flat manifolds of nonnegative scalar curvature that are also harmonically …
Convex Polygons with Parallel Opposite Sides: Convergence, Reconstruction, and Isoperimetric Inequalities
研究具有平行对边的凸多边形（CPPOS）的仿射λ-等距线，建立与光滑凸曲线的联系，给出从Wigner焦散和中心对称集重构CPPOS的条件，并证明离散改进等周不等式及面积估计。
We prove that the isoperimetric inequality due to Hersch-Payne-Schiffer for the n-th nonzero Steklov eigenvalue of a bounded simply-connected planar domain is sharp for all n=1,2,... The equality is attained in the limit by a sequence of simply-connected domains degenerating to the disjoint union of n identical disks. We give a new proof of this inequality for n=2 and show that it is strict in this case. Related results are also obtained for the product of two consecutive Steklov eigenvalues.
We formulate a plausible conjecture for the optimal Ehrhard-type inequality for convex symmetric sets with respect to the Gaussian measure. Namely, letting $J_{k-1}(s)=\int^s_0 t^{k-1} e^{-\frac{t^2}{2}}dt$ and $c_{k-1}=J_{k-1}(+\infty)$, we conjecture that the function $F:[0,1]\rightarrow\mathbb{R},$ given by $$F(a)= \sum_{k=1}^n 1_{a\in E_k}\cdot(β_k J_{k-1}^{-1}(c_{k-1} a)+α_k)$$ (with an appropriate choice of a decomposition $[0,1]=\cup_{i} E_i$ and coefficients $α_i, β_i$) satisfies, for all symmetric convex sets $K$ and $L,$ and any $λ\in[0,1]$, $$ F\left(γ(λK+(1-λ)L)\right)\geq λF\left(…
Given a simple closed plane curve $Γ$ of length $L$ enclosing a compact convex set $K$ of area $F$, Hurwitz found an upper bound for the isoperimetric deficit, namely $L^2-4πF\leq π|F_{e}|$, where $F_{e}$ is the algebraic area enclosed by the evolute of $Γ$. In this note we improve this inequality finding strictly positive lower bounds for the deficit $π|F_{e}|-Δ$, where $Δ=L^{2}-4πF$. These bounds involve wether the visual angle of $Γ$ or the pedal curve associated to $K$ with respect to the Steiner point of $K$ or the $\mathcal{L}^{2}$ distance between $K$ and the Steiner disk of $K$. For ea…
The Positive Mass Theorem implies that any smooth, complete, asymptotically flat 3-manifold with non-negative scalar curvature which has zero total mass is isometric to (R^3, delta_{ij}). In this paper, we quantify this statement using spinors and prove that if a complete, asymptotically flat manifold with non-negative scalar curvature has small mass and bounded isoperimetric constant, then the manifold must be close to (R^3,delta_{ij}), in the sense that there is an upper bound for the L^2 norm of the Riemannian curvature tensor over the manifold except for a set of small measure. This curvat…
Upper bound for the first $p$-Steklov eigenvalue in $\mathbb{R}^n$
研究 \(\mathbb{R}^n\) 中有界凸域 \(\Omega\) 的第一个 \(p -\) 斯捷克洛夫特征值，通过证明相关不等式并结合等周不等式得出明确上界，还得到了 \(p -\) 拉普拉斯算子在凸域上第一个温茨尔特征值的上界。
In [5] Herzlich proved a new positive mass theorem for Riemannian 3-manifolds $(N, g)$ whose mean curvature of the boundary allows some positivity. In this paper we study what happens to the limit case of the theorem when, at a point of the boundary, the smallest positive eigenvalue of the Dirac operator of the boundary is strictly larger than one-half of the mean curvature (in this case the mass $m(g)$ must be strictly positive). We prove that the mass is bounded from below by a positive constant $c(g), m(g) \geq c(g)$, and the equality $m(g) = c(g)$ holds only if, outside a compact set, $(N,…
Convexity on manifolds without focal points and applications
本文研究了无焦点点的黎曼流形上的严格凸函数，通过几何定义的凸函数推导出如等周轮廓函数连续性等结论，并在Kähler流形上获得Stein性质和度量球体积增长的下界。主要应用涉及拉普拉斯算子的谱，证明了在径向曲率非正的条件下，绝对连续部分谱包含无限区间，并利用无穷远处的几何构造严格凸函数，最终证明了Cheeger常数与体积熵的相等性。
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