Renata Grimaldi, Pierre Pansu
We equip many non compact non simply connected surfaces with smooth Riemannian metrics whose isoperimetric profile is smooth, a highly non generic property. The computation of the profile is based on a calibration argument, a rearrangement argument, the Bol-Fiala curvature dependent inequality, together with new results on the profile of surfaces of revolution and some hardware know-how.
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The first known example of a complete Riemannian manifold whose isoperimetric profile is discontinuous is given.
It is shown that, in dimensions $<8$, isoperimetric profiles of compact real analytic Riemannian manifolds are semi-analytic.
We show that smooth isoperimetric profiles are exceptional for real analytic Riemannian manifolds. For instance, under some extra assumption, this can happen only on topological spheres.
We show that there is a complete connected 2-dimensional Riemannian manifold with discontinuous isoperimetric profile, answering a question of Nardulli and Pansu.
In the main theorem of this paper we treat the problem of existence of minimizers of the isoperimetric problem under the assumption of small volumes. Applications of the main theorem to asymptotic expansions of the isoperimetric problem are given.
The relative isoperimetric profile of a unit square with a central square removed
本研究精确计算了移除中心正方形的单位正方形的相对等周剖面，提供了界定任意面积的最小相对周长函数。
We estimate from below the isoperimetric profile of $S^2 \times \re^2$ and use this information to obtain lower bounds for the Yamabe constant of $S^2 \times \re^2$. This provides a lower bound for the Yamabe invariants of products $S^2 \times M^2$ for any closed Riemann surface $M$. Explicitly we show that $Y(S^2 \times M^2) > (2/3) Y(S^4)$.
Remarks on the relative isoperimetric profile of polygonal domains in $\mathbb{R}^2$
本文开发了解决 $\mathbb{R}^2$ 中多边形区域相对等周问题的技术，特别关注角点，并应用于求解移除一个正方形角点的正方形的相对等周问题。
Isoperimetric profile function comparisons with Integral Ricci curvature bounds
本文在具 Ricci 曲率积分界的流形中证明了等周轮廓函数的比较结果，并推广了 Ni、Wang、Bayle 和 Rosales 在逐点曲率界下的工作。
We show that the isoperimetric profile $h_{g(t)}(ξ)$ of a compact Riemannian manifold $(M,g)$ is jointly continuous when metrics $g(t)$ vary continuously. We also show that, when $M$ is a compact surface and $g(t)$ evolves under normalized Ricci flow, $h^2_{g(t)}(ξ)$ is uniform Lipschitz continuous and hence $h_{g(t)}(ξ)$ is uniform locally Lipschitz continuous.
We construct sequences of `expander manifolds' and we use them to show that there is a complete connected 2-dimensional Riemannian manifold with discontinuous isoperimetric profile, answering a question of Nardulli and Pansu. Using expander manifolds in dimension 3 we show that for any $ε, M>0$ there is a Riemannian 3-sphere $S$ of volume 1, such that any (not necessarily connected) surface separating $S$ in two regions of volume greater than $ε$, has area greater than $M$.
Lower bounds for isoperimetric profiles and Yamabe constants
该研究估计了紧流形与欧氏空间的黎曼乘积的等周剖面显式下界，针对大体积区域给出新下界并改进了多个球面与欧氏空间乘积情形的已有估计，还将结果用于改进部分流形的Yamabe不变量下界。
The subject of these Notes is the new proof, proposed in [F. H{é}lein, In{é}galit{é} isop{é}rim{é}trique et calibrations, Annales de l'Institut Fourier 44, 4 (1994), 1211-1218] of the classical isoperimetric inequality in the plane. This proof is far from being the first one, but its interest is that it uses essentially integration by parts and Stoke's formula in a simple manner, like in a calibration. Here we expound again this proof and discuss in which sense our proof works like a calibration, or it can be understood in the framework of the theory of null Lagrangians, which goes back to Wei…
We show that, the solutions of the isoperimetric problem for small volumes are $C^{2,α}$-close to small spheres. On the way, we define a class of submanifolds called pseudo balls, defined by an equation weaker than constancy of mean curvature. We show that in a neighborhood of each point of a compact riemannian manifold, there is a unique family concentric pseudo balls which contains all the pseudo balls $C^{2,α}$-close to small spheres. This allows us to reduce the isoperimetric problem for small volumes to a variational problem in finite dimension.
In the context of sub-Riemannian Heisenberg groups Hn, n \geq 1, we shall study Isoperimetric Profiles, which are closed compact hypersurfaces having constant horizontal mean curvature, very similar to ellipsoids. Our main goal is to study the stability of Isoperimetric Profiles.
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].
We prove that the isoperimetric profile of a convex domain $Ω$ with compact closure in a Riemannian manifold $(M^{n+1},g)$ satisfies a second order differential inequality which only depends on the dimension of the manifold and on a lower bound on the Ricci curvature of $Ω$. Regularity properties of the profile and topological consequences on isoperimetric regions arise naturally from this differential point of view. Moreover, by integrating the differential inequality we obtain sharp comparison theorems: not only can we derive an inequality which should be compared with Lévy-Gromov Inequality…
For a complete noncompact connected Riemannian manifold with bounded geometry, we prove the existence of isoperimetric regions in a larger space obtained by adding finitely many limit manifolds at infinity. As one of many possible applications, we extend properties of the isoperimetric profile from compact manifolds to such noncompact manifolds.
Let $M$ be a complete Riemannian manifold possessing a strictly convex Lipschitz continuous exhaustion function. We show that the isoperimetric profile of $M$ is a continuous and non-decreasing function. Particular cases are Hadamard manifolds and complete non-compact manifolds with strictly positive sectional curvatures.
We prove a comparison theorem for the isoperimetric profiles of simple closed curves evolving by the normalized curve shortening flow: If the isoperimetric profile of the region enclosed by the initial curve is greater than that of some `model' convex region with exactly four vertices and with reflection symmetry in both axes, then the inequality remains true for the isoperimetric profiles of the evolved regions. We apply this using the Angenent solution as the model region to deduce sharp time-dependent upper bounds on curvature for arbitrary embedded closed curves evolving by the normalized …
After introducing the sub-Riemannian geometry of the Heisenberg group Hn, n \geq 1, we recall some basics about hypersurfaces endowed with the H-perimeter measure and horizontal Green's formulas. Then, we describe a class of compact closed hypersurfaces of constant horizontal mean curvature called "Isoperimetric Profiles"(they are not CC-balls!); see Section 2.1. Our main purpose is to study a closed eigenvalue problem on Isoperimetric Profiles, i.e. LHS ϕ+ λϕ= 0, where LHS is a 2nd order horizontal tangential operator analogous to the Laplace-Beltrami operator; see Section 1.5. This is done s…
On clusters and the multi-isoperimetric profile in Riemannian manifolds with bounded geometry
本文在具有有界几何的完备黎曼流形中证明等周簇的存在性、紧性及有界性，引入并证明多重等周剖面的Hölder连续性，从而将经典等周问题推广到黎曼等周簇背景。
On the Isoperimetric Profile of the Hypercube
本文证明了体积接近1/2的超立方体子集相对周长至少为1，解决了Brezis-Bruckstein猜想，并证明超立方体等周剖面不收敛于高斯等周剖面。
A comparison theorem for the isoperimetric profile on the universal cover of surfaces evolving by normalised Ricci flow is proven. For any initial metric, a model comparison is constructed that initially lies below the profile of the initial metric and which converges to the profile of the constant curvature metric. The comparison theorem implies that the evolving metric is bounded below by the model comparison for all time and hence converges to the constant curvature profile. This yields a curvature bound and a bound on the isoperimetric constant, leading to a direct proof that the metric co…
We prove a comparison theorem for the isoperimetric profiles of solutions of the normalized Ricci flow on the two-sphere: If the isoperimetric profile of the initial metric is greater than that of some positively curved axisymmetric metric, then the inequality remains true for the isoperimetric profiles of the evolved metrics. We apply this using the Rosenau solution as the model metric to deduce sharp time-dependent curvature bounds for arbitrary solutions of the normalized Ricci flow on the two-sphere. This gives a simple and direct proof of convergence to a constant curvature metric without…
We consider the problem of minimizing the relative perimeter under a volume constraint in an unbounded convex body $C\subset \mathbb{R}^{n+1}$, without assuming any further regularity on the boundary of $C$. Motivated by an example of an unbounded convex body with null isoperimetric profile, we introduce the concept of unbounded convex body with uniform geometry. We then provide a handy characterization of the uniform geometry property and, by exploiting the notion of asymptotic cylinder of $C$, we prove existence of isoperimetric regions in a generalized sense. By an approximation argument we…
In this paper we consider the isoperimetric profile of convex cylinders $K\times\mathbb{R}^q$, where $K$ is an $m$-dimensional convex body, and of cylindrically bounded convex sets, i.e, those with a relatively compact orthogonal projection over some hyperplane of $\mathbb{R}^{n+1}$, asymptotic to a right convex cylinder of the form $K\times\mathbb{R}$, with $K\subset\mathbb{R}^n$. Results concerning the concavity of the isoperimetric profile, existence of isoperimetric regions, and geometric descriptions of isoperimetric regions for small and large volumes are obtained.
Let $(T^k,h_k)=(S_{r_1}^1\times S_{r_2}^1 \times ... \times S_{r_k}^1, dt_1^2+dt_2^2+...+dt_k^2)$ be flat tori, $r_k\geq ...\geq r_2\geq r_1>0$ and $(\mathbb R^n,g_E)$ the Euclidean space with the flat metric. We compute the isoperimetric profile of $(T^2\times \mathbb R^n, h_2+g_E)$, $2\leq n\leq 5$, for small and big values of the volume. These computations give explicit lower bounds for the isoperimetric profile of $T^2\times\mathbb R^n$. We also note that similar estimates for $(T^k\times \mathbb R^n, h_k+g_E)$, $2\leq k\leq5$, $2\leq n\leq 7-k$, may be computed, provided estimates for $(T…
Isoperimetric estimates in the product of small and large volume manifolds
研究通过分析小体积和大体积流形的乘积，推导出等周轮廓的下界，并证明在特定条件下存在等周区域。
Isoperimetric problem and structure at infinity on Alexandrov spaces with nonnegative curvature
研究非负曲率有限维Alexandrov空间的等周剖面、等周集存在性与无穷远渐近结构的关系，证明线性体积增长等条件的等价性，并给出2维情形下等周集的存在性与拓扑刻画。
We show that the Cheeger constant of compact surfaces is bounded by a function of the area. We apply this to isoperimetric profiles of bounded genus non-compact surfaces, to show that if their isoperimetric profile grows faster than $\sqrt t$, then it grows at least as fast as a linear function. This generalizes a result of Gromov for simply connected surfaces. We study the isoperimetric problem in dimension 3. We show that if the filling volume function in dimension 2 is Euclidean, while in dimension 3 is sub-Euclidean and there is a $g$ such that minimizers in dimension 3 have genus at most …
We reinterpret the renormalized volume as the asymptotic difference of the isoperimetric profiles for convex co-compact hyperbolic 3-manifolds. By similar techniques we also prove a sharp Minkowski inequality for horospherically convex sets in $\mathbb{H}^3$. Finally, we include the classification of stable constant mean curvature surfaces in regions bounded by two geodesic planes in $\mathbb{H}^3$ or in cyclic quotients of $\mathbb{H}^3$.
Sharp isoperimetric comparison on non-collapsed spaces with lower Ricci bounds
本文针对具有下Ricci曲率界的非光滑RCD空间，通过原创变分估计与渐近质量分解方法，证明了尖锐等周比较定理与等周轮廓的维数凹性，推广了紧流形及欧氏凸体上的经典结果。
Volume spectrum of fiber bundles and the widths of Berger spheres
本文证明纤维丛体积谱的上界不等式，并推广至相变谱，进而计算 Berger 球面的低宽度，揭示赤道球面在两种设定下达到特定宽度而非更低宽度。
Rigidity and large volume residues in exterior isoperimetry for convex sets
本文利用“渐近维数”概念刻画了外部等周剖面与半空间相等的凸体，并证明了当渐近维数较低时大体积下剖面渐近于全空间，同时给出了相应误差的幂律估计。
Sharp Gaussian Isoperimetry along a Ricci Flow
本文通过单调性公式证明了沿里奇流的共轭热核测度的锐利高斯等周不等式，并由此得到了精确的高斯扩展定理和高斯-量纲双集集中估计，恢复了Hein-Naber的指数集中估计，同时推导了高斯排列不等式，恢复了Hein-Naber的尖锐对数 Sobolev 不等式，并识别了Bamler的L^p-Poincaré不等式中的通用高斯模型常数。
Asymptotic isoperimetry on non collapsed spaces with lower Ricci bounds
该文研究N维${\rm RCD}(K,N)$空间的等周比较定理与渐近等周性质，得到几乎正则性定理及函数不等式推论，多数结论在光滑非紧流形经典框架下也为新结果，合成理论起关键作用。
On the Hamilton's isoperimetric ratio in complete Riemannian manifolds of finite volume
本文研究有限体积完备黎曼流形中 Hamilton 等周比问题，证明了分离区域的存在性，并利用几何测度论与 Ascoli-Arzela 定理将高维极小化问题归结为等周剖面的辅助问题，从而规避了传统的缩短曲线流方法。
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