论文标题
与坐标的简单重力
Simplicial Gravity with Coordinates
论文作者
论文摘要
我们提出了regge演算的表述,其中任意坐标与简单复合物的每个顶点相关联,并且自由度由每个单纯形上的度量标准给出。因此,在相应的度量转换后,在离散坐标集的任意变换下确定边缘的长度并在离散坐标集的任意变换下保持不变。坐标转换下的不变性需要张量计算,我们的表述紧密遵循连续理论的通常形式主义。平行运输,克里斯托佛尔符号,协变量衍生物和黎曼曲率张量的定义以一种自然的方式遵循。在此信件中,爱因斯坦的动作变成了Regge Action,其赤字角度$θ$取代了$ \sinθ$。与连续理论的对应关系可以扩展到具有曲率张量的较高功能,Vielbein形式主义以及重力与物质领域的耦合(标量,费尔米电场,包括旋转$ 3/2 $ coguge磁场)的作用,然后在本文中确定并在本文中进行了讨论。在此上下文中,在$ 4 $尺寸的$ n = 1 $ supergravity上对简单晶格的操作。另一个恢复的结果是,即使在没有重力的情况下,Yang-Mills在简单晶格上的作用也是两个plaquettes术语的组成,这与对高皮块晶格的一个plaquette wilson作用不同。还试图制定一个离散的微积分,以包括高阶的差异形式和在此方案中的自由差分代数的测量。但是,这导致形成不满足$ d $运营商的关联和分配法的产品。在雷格微积分的背景下,仍缺乏包含高阶差异形式的理论的适当表述。
We present a formulation of Regge Calculus where arbitrary coordinates are associated to each vertex of a simplicial complex and the degrees of freedom are given by the metric on each simplex. The lengths of the edges are thus determined and are left invariant under arbitrary transformations of the discrete set of coordinates, provided the metric transforms accordingly. Invariance under coordinate transformations entails tensor calculus and our formulation follows closely the usual formalism of the continuum theory. The definitions of parallel transport, Christoffel symbol, covariant derivatives and Riemann curvature tensor follow in a rather natural way. In this correspondence Einstein action becomes Regge action with the deficit angle $θ$ replaced by $\sin θ$. The correspondence with the continuum theory can be extended to actions with higher powers of the curvature tensor, to the vielbein formalism and to the coupling of gravity with matter fields (scalars, fermionic fields including spin $3/2$ fields and gauge fields) which are then determined unambiguously and discussed in the paper. An action on the simplicial lattice for $N=1$ supergravity in $4$ dimensions is derived in this context. Another relavant result is that Yang-mills actions on a simplicial lattice consist, even in absence of gravity, of two plaquettes terms, unlike the one plaquette Wilson action on the hypercubic lattice. An attempt is also made to formulate a discrete differential calculus to include differential forms of higher order and the gauging of free differential algebras in this scheme. However this leads to form products that do not satisfy associativity and distributive law with respect to the $d$ operator. A proper formulation of theories that contain higher order differential forms in the context of Regge Calculus is then still lacking.