Theoretical and observational aspects of the variation of fundamental constants of Nature

  1. Albareti, Franco Dante
Dirigida por:
  1. Antonio López Maroto Director
  2. Francisco Prada Martínez Director/a

Universidad de defensa: Universidad Autónoma de Madrid

Fecha de defensa: 14 de enero de 2019

Tipo: Tesis

Resumen

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 encode new phenomena yet to be discovered. In recent years, an enormous observational effort has been devoted to study the possible variation in space and time of some of these fundamental constants. Such a discovery would have deep consequences in our current models for physical interactions, and in particular for the theoretical framework behind gravitation. Astrophysics and Cosmology provide us with a great window to look for any variation, with space and time scales ranging from the Solar System to the whole observable Universe and its origin. On the other side, theoretical models to accommodate variation of fundamental constants are also being actively explored. This thesis is divided into an observational analysis and a theoretical study. First, we present the most precise observational constraint to date for the cosmological variation of the fine structure constant using emission lines present in quasar spectra up to redshift z = 1. From the Sloan Digital Sky Survey Quasar Catalog (Data Release 12), we build a sample of 13 175 quasar spectra showing the [O iii] doublet ( 4960; 5008 Å). Then, by measuring the separation between both lines we obtain the following relative constraint on the time variation of the fine structure constant = ¹0:9 1:8º 105. We also impose limits on its variation in redshift bins ( z 0:06) over the last 7.9 Gyr at the 104 level. Several sources of systematics are analyzed including sky contamination and line blendings. In the second part, we explore a theoretical mechanism producing expectations values of scalar fields to depend on the gravitational potential. To have varying expectation values is one of the usual ways to accommodate variation of fundamental constants. We develop a formalism that enables us to compute the complete one-loop quantum corrections to the effective potential and energy momentum tensor of scalar fields arising in the presence of gravity. This formalism provides the local part, usually computed with the well-known DeWitt-Schwinger expansion, but it would also allow to obtain the non-local contributions. Assuming weak and slowly varying gravitational fields, we obtain a complete set of mode solutions for the Klein-Gordon equation in perturbed Friedmann-Robertson-Walker geometries at leading order in the adiabatic approximation. Then, we compute the corresponding expectation values of a self-interacting scalar field as a mode summation in different quantum states and apply dimensional regularization to obtain the final contributions. Although there is no effect due to metric perturbation in vacuum states, there are thermal corrections that could modify the expectation value of scalar fields