Structure and Statistics of Disordered Systems

在复杂网络建模中经常遇到的一个挑战是，仅知道系统的微观规则就预测宏观结果。例子从全球层面（社交网络、经济网络）到细胞层面（免疫网络、神经元网络），可以是虚拟的，而不是物理的（信号处理、人工智能）。概率论可以通过利用越来越多的随机变量的聚集效应的预测能力来分析这些系统，也就是所谓的无序。为了有效地利用这一理论，数学家和其他从业者必须能够从更容易测量的系统统计数据中推断出定性的大尺度结构，并确定这些统计数据与控制模型的参数之间的关系。这个项目将为两类无序系统追求这些目标：自旋玻璃和随机生长，这两类系统都是物理学，计算机科学和工程学的持续兴趣。该项目将包括为研究生和本科生提供研究培训机会，并为小学生和中学生开展外联工作。其中包括：（1）利用泛函分析和偏微分方程的技巧，建立了多粒子和矢量自旋模型的极限能量的Parisi型公式，（2）通过对得到的Parisi公式进行变分计算，确定了这些模型的相图;（3）通过调整随机分析工具，对与第一次和最后一次渗流有关的生长界面波动的大小作出新的估计;和（4）研究定向聚合物中的淬灭局域化现象，通过利用未开发的连接到自旋玻璃理论。这项严格的数学工作将得到实验计算机模拟的帮助。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

A recurring challenge in modeling complex networks is to predict macroscopic outcomes from knowing only the microscopic rules of a system. Examples range from the global level (social networks, economic networks) to the cellular level (immune networks, neuron networks), and can be virtual rather than physical (signal processing, artificial intelligence). Probability theory can analyze these systems by harnessing the predictive power of the aggregate effect of more and more random variables, otherwise known as disorder. To make effective use of this theory, mathematicians and other practitioners must be able to both infer qualitative large-scale structure from more easily measured system statistics and identify the relationship between these statistics and the parameters governing the model. This project will pursue these objectives for two classes of disordered systems: spin glasses and random growth, both of which are of continuing interest in physics, computer science, and engineering. The project will include research training opportunities for graduate and undergraduate students and also outreach efforts to elementary and secondary students. Among the proposed investigations are (1) establishing Parisi-type formulas for the limiting energy of so-called multi-species and vector-spin models, by using techniques from functional analysis and PDEs; (2) determination of the phase diagram of these same models, by performing variational calculus on the obtained Parisi formulas; (3) producing new estimates on the size of fluctuations in growth interfaces associated to first- and last-passage percolation, by adapting tools from stochastic analysis; and (4) studying the phenomenon of quenched localization in directed polymers, by leveraging untapped connections to spin glass theory. This rigorous mathematical work will be aided by experimental computer simulation.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.