Geometric Flows and Analysis on Metric Spaces

该项目的第一部分涉及两个非线性偏微分方程式，它们出现在科学和工程的一些不同学科中，以及数学内部。这些方程描述了随着时间的推移，为了尽可能有效地简化其形状而演变的曲面或曲面对象的运动。一个重要的特征是奇点的形成。奇点使解决方案能够对拓扑变化的情况进行建模，例如，当一个肥皂泡拉长并分裂成两个气泡时。一方面，这种灵活性导致了无数深刻的应用；另一方面，它带来了巨大的智力挑战，这已经占据了数学家40多年的时间。拟议的研究旨在以过去几年的成功为基础，解决一些主要的公开问题。该项目的第二部分应用几何学和分析的思想来研究粗糙物体的结构，包括分形学。这一领域在过去20年里发展非常迅速，这是由于数学不同部分之间的新联系，以及计算机科学对问题的应用。该项目还包括对博士生的大量培训。该项目旨在研究热方程的两个非线性类似物：平均曲率曲面的演化和汉密尔顿的Ricci流。平均曲率演化作为一种自然的表面界面演化模型已经被研究了几十年。Ricci流描述了一种演化的几何，并被用在Perelman的Poincare猜想的解中。拟对这些方程进行研究的主要目的是研究与其解的奇性形成有关的问题，包括其结构和稳定性。几何和拓扑学中基本猜想的解决是这项工作的结果。研究计划的另一个组成部分是利用最近几年发展起来的分析工具，对具有自相似或分形特征的空间进行调查。这里的目标之一是如果可能的话，将空间变形为最佳形式，以便揭示隐藏的对称性，否则就表明不存在隐藏的对称性。这对于理解无限群的渐近形状是非常有用的，也是过去15-20年来几个研究趋势汇合的一部分。类似想法的另一个应用是在理论计算机科学中嵌入问题：Cheeger，Naor和PI能够实质上改进先前关于负型空间嵌入的最著名结果，与Goemans-Linial猜想的量化版本有关。这个项目专门研究几何演化方程、嵌入问题、度量空间分析和几何群论。项目中的演化方程为平均曲率流和Ricci流。度量空间簇在三个方面的分析研究：(1)bilipschitz嵌入问题及相关问题，(2)满足Poincare不等式的空间结构，(3)Gromov双曲空间的边界结构。这三个领域的共同主题是满足庞加莱不等式的空间，以及重新调整导致单一极限空间的论点。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The first part of the project involves two nonlinear partial differential equations that arise in a number of different disciplines in science and engineering, as well as from within mathematics. These equations describe the motion of a curved surface or curved object which evolves so as to simplify its shape as efficiently as possible over time. An important feature is the formation of singularities. Singularities are what enable the solutions to model situations where topology changes, for example when a soap bubble elongates and splits into two bubbles. On the one hand, this flexibility has led to numerous profound applications; on the other, it creates great intellectual challenges which have occupied mathematicians for more than 40 years. The proposed research aims to build on successes in the last few years, to address some of the main open problems. The second part of the project applies ideas from geometry and analysis to study the structure of rough objects, including fractals. This area has been developing very rapidly in the last 20 years, due to new connections between different parts of mathematics, and applications to problems from computer science. The project also involves substantial training of PhD students.The project aims to study two nonlinear analogs of the heat equation: evolution of surfaces by mean curvature, and Hamilton's Ricci flow. Evolution by mean curvature has been studied for decades as a natural model for evolving surface interfaces. Ricci flow describes an evolving geometry, and was used in Perelman's solution of the Poincare conjecture. The primary objective of the proposed research on these equations is to study issues related to the formation of singularities in their solutions, including their structure and stability. The resolution of fundamental conjectures in geometry and topology is an outgrowth of this work. Another component of the research program is an investigation of spaces which have a self-similar or fractal character, using analytic tools that have been developed in the last few years. Here one of the goals is to deform the space into an optimal form, if possible, in order to reveal hidden symmetries, and otherwise show that no hidden symmetries exist. This is very useful for understanding the asymptotic shape of infinite groups, and is part of confluence of several research trends over the last 15-20 years. Another application of similar ideas is to embedding problems in theoretical computer science: Cheeger, Naor, and the PI were able to substantially improve the previous best known results on the embedding of spaces of negative type, in connection with the quantitative version of the Goemans-Linial conjecture. This project specifically addresses geometric evolution equations, embedding problems, analysis on metric spaces, and geometric group theory. The evolution equations in the project are mean curvature flow and Ricci flow. The research in analysis on metric spaces clusters in three areas: (1) bilipschitz embedding problems and related issues, (2) the structure of spaces satisfying Poincare inequalities, (3) the structure of boundaries of Gromov hyperbolic spaces. Common themes in all three areas are spaces satisfying Poincare inequalities, and rescaling arguments leading to singular limit spaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.