Observables and gauge invariance in the theory of nonlinear spacetime perturbations

被引:41
作者
Bruni, M [1 ]
Sonego, S
机构
[1] Cardiff Univ, Dept Phys & Astron, Cardiff CF2 3YB, S Glam, Wales
[2] Univ Udine, DIC, I-33100 Udine, Italy
关键词
D O I
10.1088/0264-9381/16/7/101
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We discuss the issue of observables in general-relativistic perturbation theory, adopting the view that any observable in general relativity is represented by a scalar field on spacetime. In the context of perturbation theory, an observable is therefore a scalar field on the perturbed spacetime, and as such is gauge invariant in an exact sense (to all orders), as one would expect. However, perturbations are usually represented by fields on the background spacetime, and expanded at different orders into contributions that may or may not be gauge independent. We show that perturbations of scalar quantities are observable if they are first-order gauge invariant, even if they are gauge dependent at higher order. Gauge invariance to first order therefore plays an important conceptual role in the theory, for it selects the perturbations with direct physical meaning from those having only a mathematical status. The so-called 'gauge problem', and the relationship between measured fluctuations and gauge-dependent perturbations that are computed in the theory are also clarified.
引用
收藏
页码:L29 / L36
页数:8
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