Theoretical and observational aspects of the variation of fundamental constants of Nature
Author
Albareti, Franco DanteEntity
UAM. Departamento de Física TeóricaDate
2019-01-14Subjects
Teoría cuántica de campos - Tesis doctorales; Cuásares - Tesis doctorales; Espectroscopía astronómica - Tesis doctorales; FísicaNote
Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 14-01-2019Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
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 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 10��������5. We also impose limits on its variation in redshift bins ( z 0:06)
over the last 7.9 Gyr at the 10��������4 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
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