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arXiv 1703.04541hep-thmath.AGmath.CO
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正几何与标准形

Positive Geometries and Canonical Forms

Nima Arkani-Hamed, Yuntao Bai, Thomas Lam

摘要:

近年来,散射振幅物理学与一类数学对象--正格拉斯曼、正环格拉斯曼、树和环振幅面体--之间出现了令人惊讶的联系,它们被松散地称为“正几何”。几何和物理之间的联系是由一个唯一的微分形式提供的,该微分形式由空间的所有边界上(仅)具有对数奇点的性质正则地确定,每个边界上的余数由该边界上的正则形式给出。在本文中,我们开始探索“正几何”和“标准形式”作为研究对象在自己的权利,在一个更一般的数学设置。我们给出了一个精确的定义,积极的几何形状和规范形式,介绍了一般的方法,寻找形式更复杂的积极的几何形状从简单的,并提出了许多例子,积极的几何形状在射影空间,格拉斯曼,复曲面,集群和旗品种。我们还说明了一些战略计算规范的形式,产生有趣的陈述形式与广泛的正几何类,从最简单的振幅面体的体积的任意凸多面体的新表达式。

英文摘要:

Recent years have seen a surprising connection between the physics of scattering amplitudes and a class of mathematical objects--the positive Grassmannian, positive loop Grassmannians, tree and loop Amplituhedra--which have been loosely referred to as "positive geometries". The connection between the geometry and physics is provided by a unique differential form canonically determined by the property of having logarithmic singularities (only) on all the boundaries of the space, with residues on each boundary given by the canonical form on that boundary. In this paper we initiate an exploration of "positive geometries" and "canonical forms" as objects of study in their own right in a more general mathematical setting. We give a precise definition of positive geometries and canonical forms, introduce general methods for finding forms for more complicated positive geometries from simpler ones, and present numerous examples of positive geometries in projective spaces, Grassmannians, and toric, cluster and flag varieties. We also illustrate a number of strategies for computing canonical forms which yield interesting representations for the forms associated with wide classes of positive geometries, ranging from the simplest Amplituhedra to new expressions for the volume of arbitrary convex polytopes.

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