Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geodesic-light-cone coordinates and the Bianchi I spacetime   The geodesic-light-cone (GLC) coordinates are a useful tool to analyse light
propagation and observations in cosmological models. In this article, we
propose a detailed, pedagogical, and rigorous introduction to this coordinate
system, explore its gauge degrees of freedom, and emphasize its interest when
geometric optics is at stake. We then apply the GLC formalism to the
homogeneous and anisotropic Bianchi I cosmology. More than a simple
illustration, this application (i) allows us to show that the Weinberg
conjecture according to which gravitational lensing does not affect the proper
area of constant-redshift surfaces is significantly violated in a globally
anisotropic universe; and (ii) offers a glimpse into new ways to constrain
cosmic isotropy from the Hubble diagram.

20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs