RUI: Flows of G2-Structures on Manifolds

最持久的科学问题之一是了解宇宙的性质和支配它的规律。自从爱因斯坦提出广义相对论以来，人们就认识到物理学和宇宙几何之间有着非常密切的联系。然而，最近的物理理论，如超弦理论和m理论，表明四维时空的物理特性可以用隐藏的六维或七维空间的几何来描述。在这个项目中，PI将研究这些理论中出现的一种特殊的七维空间的性质，称为具有g2结构的流形。该项目的主要目标是进一步发展g2结构的变形或“流动”理论，这将影响不同类别的g2结构之间的平滑过渡。PI预计这将为无扭转g2结构存在的充分条件铺平道路，这是微分几何中最重要的开放问题之一。(g2结构在流形的每个点上定义了向量的“点积”——一种将两个向量相乘得到标量的方法——以及允许将两个向量相乘得到第三个向量的“叉积”。无扭g2结构是那些点积和叉积最大程度相容的结构。作为项目的一部分，PI将培训本科生研究助理，并让他们参与实验代数与几何实验室的活动，PI是该实验室的联合主任。该实验室的活动将结合培训、指导、研究和推广，以促进各个层次的数学——从K-12开始，到更广泛的社区，一直到研究生水平。在他之前的工作中，PI引入了共闭g2结构的修正拉普拉斯共流，修正了标准拉普拉斯共流的非抛物性。PI还从八元束的角度介绍了g2结构的描述，将g2结构的扭转解释为八元束连接，并在同一度量类中选择g2结构作为规范的选择。然后将具有无散度扭转的g2结构解释为能量泛函的临界点，并作为库仑规范的模拟。这个项目建立在之前的工作基础上。主要目的是证明标准拉普拉斯共流的存在性。这将首先通过使用调和映射技术证明在固定度量类中具有无发散扭转的g2结构的存在性来实现。然后，这将被用作拉普拉斯共流的量规固定条件，这将把它与已知存在的修正共流联系起来。本项目的第二个目标是研究和构建其他重要的g2结构流，目的是证明在适当条件下的存在性和稳定性，并分析这些流在齐次流形上的行为。本课题的第三个目标是研究八元束值微分形式的性质，并得到Dolbeault上同的八元值模拟。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

One of the most enduring scientific problems is to understand the properties of the universe and the laws that govern it. Ever since Einstein's theory of general relativity, it was understood that there is a very close link between the physics and the geometry of the universe. However, most recent physical theories, such as superstring theory and M-theory, show that the physical properties of 4-dimensional spacetime may be described in terms of the geometry of hidden six- or seven-dimensional spaces. In this project, the PI will study the properties of a particular kind of seven-dimensional spaces which appear in these theories, known as manifolds with a G2-structure. The main goal of this project is to further develop the theory of deformations or `flows' of G2-structures which will effect smooth transitions between different classes of G2-structures. The PI anticipates that this will pave the way towards giving sufficient conditions for existence of torsion-free G2-structures, which is one of the most significant open problems in differential geometry. (A G2-structure defines, at each point of the manifold, a `dot product' of vectors -- a way of multiplying two vectors to get a scalar -- as well as a `cross product' that allows one to multiply two vectors to produce a third vector. Torsion-free G2-structures are those for which these dot and cross products are maximally compatible.) As part of the project, the PI will train undergraduate research assistants and will involve them in the activities of the Experimental Algebra & Geometry Lab, of which the PI is a co-director. The lab's activities will combine training, mentoring, research, and outreach to promote mathematics at various levels -- starting at K-12, the broader community, and going all the way to graduate level.In his prior work, the PI introduced the modified Laplacian coflow of co-closed G2-structures that rectified the non-parabolicity of the standard Laplacian coflow. The PI also introduced a description of G2-structures in terms of octonion bundles that interpreted the torsion of a G2-structure as an octonionic connection and the choice of a G2-structure within the same metric class as a choice of gauge. G2-structures with divergence-free torsion were then interpreted as critical points of an energy functional and as an analogue of the Coulomb gauge. This project builds upon this prior work. The main goal is to prove existence properties for the standard Laplacian coflow. This will be accomplished by first proving the existence of G2-structures with divergence-free torsion within a fixed metric class using harmonic map techniques. This will then be used as a gauge-fixing condition for the Laplacian coflow, which will relate it to the modified coflow for which existence is known. The second objective of this project is to study and construct other significant flows of G2-structures, with the aim of proving existence and stability under appropriate conditions and analyzing the behavior of these flows on homogeneous manifolds. The third objective of this project is to study the properties of octonion-bundle-valued differential forms and to obtain an octonion-valued analogue of Dolbeault cohomology.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.