The impact of systematic effects on the cosmic distance ladder

• Ano de defesa: 2024
• Autor(a) principal: Petreca, Alexandra Turmina
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: abordagem f(z)CDM; escada de distâncias cósmicas; tensão de Hubble; the cosmic distance ladder; the f(z)CDM approach; the Hubble tension
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/43/43134/tde-29022024-122517/

The main objective of this work is to analyze possible residual systematic effects associated with the determination of the Hubble constant ($H_0$). This is done by investigating the problem from an experimental point of view, through analysis and modeling of real and synthetic data used as input for the cosmic distance ladder method, and from a theoretical point of view, proposing a new model for the background evolution of the Universe. In the data analysis and modeling part, synthetic data samples were generated capturing all the important features of real data coming from cepheids and type Ia supernovae (SNeIa) made available by SH0ES and Pantheon+ teams. Systematic errors were added to these samples in order to check their impact on several parameters of the cosmic distance ladder, especially on $H_0$. We verified claims in the literature that order 0.5\\% biases on apparent magnitudes of \\ac are enough to shift $H_0$ by a few $\\si{\\kilo \\meter \\per \\second \\per \\mega \\parsec}$, as long as they are not uniform across the second and third rungs of the ladder, that is, the calibration and Hubble flow samples. On the other hand, we show that $H_0$ and the absolute magnitudes of cepheids and supernovae are strongly protected against biases affecting cepheids metallicities. We also studied, using real and synthetic datasets, the impact on the distance ladder parameters of different SNeIa color correction models. Particular attention was given to a model where SNeIa from the calibration and the Hubble flow samples have different color slopes, as this effect has been recently claimed to solve the so called Hubble tension. Our results regarding such a color slope effect are inconclusive so far, but further studies are planned. Finally, a hybrid approach combining the standard cosmological model and cosmography was proposed to determine $H_0$. Three orders of the so called Padé series ($P_$, $P_$ and $P_$) were used to parameterize the dark energy density contribution to the background evolution. The constraints on the cosmological parameters were made using CosmoMC, with data from CMB, baryonic acoustic oscillations, cosmic clocks and type Ia supernovae. The values of $H_0$ obtained with this hybrid approach are consistent with the one obtained from the CMB anisotropies assuming a spatially-flat ΛCDM cosmology.