“ANÁLISES GERAIS DA VELOCIDADE DA LUZ COM OBSERVAÇÕES COSMOLÓGICAS”

Abstract

The fundamental constants of Nature play a crucial role in our understanding of the Universe. They represent the limits of our knowledge of the laws of physics, but at the same time, they systematize new phenomena yet to be discovered. In recent years, an enormous observational effort has been devoted to studying the possible variation in space and time of some of these fundamental constants. Such a discovery would have profound consequences for our current models of physical interactions and, in particular, for the theoretical framework behind gravitation. Cosmology provides us with a vast window to search for this variation, with scales of space and time ranging from the Solar System to the entire observable Universe and its origin. On the other hand, theoretical models are being actively developed in order to provide a physically viable description of the variation of fundamental constants. Therefore, measurements of fundamental physical constants using astronomical obser- vational data represent a powerful method to investigate evidence for new physics beyond the standard cosmological model, namely the ΛCDM model. In this context, we measure the speed of light c by means of the Hubble parameter and angular diameter distance measurements from current datasets, obtained from a compilation of galaxy ages and radial baryon acoustic oscillations (BAO) for the former, and Type Ia Supernova (SNe) distances from Pantheon+SH0ES for the latter. We do this by performing a Gaussian Process reconstruction of these quantities, in order to avoid the assumption of a cosmo- logical model. We then predict the accuracy of this measurement from upcoming galaxy redshift surveys, such as J-PAS, and from standard sirens from gravitational-wave exper- iments, such as LIGO and the Einstein Telescope. Our results indicate that we may be able to reduce the uncertainty of light speed measurements from approximately 5% with current data to 1.5-2% when these future data become available. Furthermore, we perform a test of the cosmic distance duality relation (CDDR), one of the most fundamental relations in Cosmology, in order to test a model of variable speed of light known as the “minimally extended varying speed of light" (meVSL). This model predicts that the speed of light varies together with other fundamental constants, in a way that preserves Lorentz invariance, thermodynamics, Bianchi identities, etc., but by modifying the duality relation mentioned above. We use different data sets of baryon acoustic oscillations from SDSS and DESI, as well as Type Ia supernovae from the Pantheon+SH0ES compilation, and Gaussian processes again to reconstruct the data of Supernovae luminosity distance. We obtained a deviation from the usual RDDC of approximately 4σ using Supernovae with a specific set of BAO data from the SDSS, which measures its transverse mode (2D). However, this result was not found in other BAO samples from the SDSS and DESI that measured its anisotropic mode (3D). This indicates to us that these data are not yet precise enough to distinguish between evidence for new physics and possible systematics errors.