How does light move in a generic metric-affine background?

Abstract

Light is the richest information retriever for most physical systems, particularly so for astronomy and cosmology, in which gravitation is of paramount importance, and also for solid state defects and metamaterials, in which some effects can be mimicked by non-Euclidean or even non-Riemannian geometries. Thus, it is expedient to probe light motion in geometrical backgrounds alternative to that of general relativity. Here we investigate this issue in generic metric-affine theories and derive (i) the expression, in the geometrical optics (eikonal) limit, for light trajectories, showing that they still are null (extremal) geodesics and thus, in general, no longer autoparallels, (ii) a generic {formula} to obtain the relation between source (galaxy) and reception (observer) angular size (area) distances, generalizing Etherington's original distance reciprocity relation (DRR), and then applying it to two particular representative non-Riemannian geometries. First in metric-compatible, completely antisymmetric torsion geometries, the generalized DRR is not changed at all, and then in Weyl integrable spacetimes, the generalized DRR assumes a specially simple expression.

6 pages, 1 figure

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• Probing the cosmic opacity from Future Gravitational Wave Standard Sirens
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• Cosmological signatures of torsion and how to distinguish torsion from the dark sector
• Strongly lensed supernovae as a self-sufficient probe of the distance duality relation
• Testing the cosmic distance duality relation with baryon acoustic oscillations and supernovae data
• Exploring the potentiality of standard sirens to probe cosmic opacity at high redshifts
• The impact of 2D and 3D BAO measurements on the Cosmic Distance Duality Relation with HII galaxies
• Constraints on the cosmic distance duality relation with simulated data of gravitational waves from the Einstein Telescope
• Resilience and implications of adiabatic CMB cooling
• Gravitational wave stochastic background in reduced Horndeski theories
• Testing the null energy condition with precise distance measurements
• From Nonparametric Distance Reconstruction to Testing the Etherington Relation and Cosmic Curvature Using 2D and 3D BAO Measurements