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arXiv 1107.0933math-phgr-qcmath.MP
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Minkowski共形无穷空间的几何与形状

Geometry and Shape of Minkowski's Space Conformal Infinity

Arkadiusz Jadczyk

摘要:

我们回顾并进一步分析了Penrose的“无穷远光锥”--Minkowski空间的共形闭包。在现有的文献中,它的几何形状和潜在的混乱的例子被指出。有人认为,这是更好地考虑共形无穷大作为一个针角超圆(或极限角环面)的家庭的圆圈,所有相交于一个,只有一个点,而不是一个'锥'。给出了一种使用圆零测地线的参数化方法。紧Minkowski空间有三种表示方式:作为酉群U(2)的群流形,作为六维实空间中的射影二次曲面,作为复四维扭量空间中的极大全迷向子空间的Grassmannian。利用共形Clifford代数Cl(4,2)在扭子上的反线性作用的具体表示,给出了这些表示之间的显式关系.时空几何的概念与李球几何的概念有明确的联系。特别地,共形无穷大忠实地由3D实空间中的平面加上无穷远点来表示。封闭零测地线被困在无穷远表示平行平面前(加上无穷远点)。一个版本的投影二次在六维空间中的商是采取正实数的显示,导致对称杜宾的类型'针角圆'形状的共形无穷大。

英文摘要:

We review and further analyze Penrose's 'light cone at infinity' - the conformal closure of Minkowski space. Examples of a potential confusion in the existing literature about it's geometry and shape are pointed out. It is argued that it is better to think about conformal infinity as of a needle horn supercyclide (or a limit horn torus) made of a family of circles, all intersecting at one and only one point, rather than that of a 'cone'. A parametrization using circular null geodesics is given. Compactified Minkowski space is represented in three ways: as a group manifold of the unitary group U(2) a projective quadric in six-dimensional real space of signature (4,2) and as the Grassmannian of maximal totally isotropic subspaces in complex four--dimensional twistor space. Explicit relations between these representations are given, using a concrete representation of antilinear action of the conformal Clifford algebra Cl(4,2) on twistors. Concepts of space-time geometry are explicitly linked to those of Lie sphere geometry. In particular conformal infinity is faithfully represented by planes in 3D real space plus the infinity point. Closed null geodesics trapped at infinity are represented by parallel plane fronts (plus infinity point). A version of the projective quadric in six-dimensional space where the quotient is taken by positive reals is shown to lead to a symmetric Dupin's type `needle horn cyclide' shape of conformal infinity.

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