Light scalar fields in a dark universe: models of inflation, dark energy and dark matter

Abstract

La teoría científica de más éxito hoy en día, sobre el origen y la evolución del universo, es conocida como el modelo estándar del Big Bang, el cual es una de las construcciones intelectuales más ambiciosas de la humanidad. Se basa en dos ramas bien consolidadas de la física teórica, a saber, la teoría de la Relatividad General y el Modelo Estándar de la física de partículas, y es capaz de hacer predicciones sólidas, como la expansión del universo, la existencia del fondo de radiación de microondas y las abundancias relativas de los elementos ligeros. Algunas de las predicciones teóricas ya han sido confirmadas por observaciones muy precisas.<br/>Según la cosmología estándar del Big Bang, el universo primitivo consistía en un plasma muy caliente y denso que se expandió y se enfrió continuamente hasta el presente, dando paso a una serie de transiciones de fase cosmológicas, donde las teorías que describen el universo en cada fase son distintas. Dado que las energías del universo primitivo fueron mucho más altas que las alcanzadas en experimentos terrestres, el estudio del universo primitivo podría ofrecernos importantes informaciones sobre nuevas interacciones y nuevas partículas, abriendo nuevas direcciones para la extensión del Modelo Estándar de la física de partículas.<br/>Como ya he mencionado anteriormente, durante la expansión del universo ocurrieron varias transiciones de fase que dejaron su huella sobre el estado presente del universo. Las observaciones sugieren que durante una de estas transiciones de fase, el universo primitivo sufrió un periodo de expansión acelerada, conocido como inflación. Aunque no forma parte de la cosmología estándar, la inflación es capaz de solucionar de una manera simple y elegante casi todos los problemas relacionados con el modelo estándar del Big Bang, y debería tenerse en cuenta en cualquier extensión posible de la teoría. Las observaciones también revelan la existencia de dos formas de energía desconocidas, a saber, materia oscura y energía oscura. La materia oscura es una forma de materia no relativista y no bariónica, que solamente puede ser detectada indirectamente, mediante su interacción con la materia normal. La energía oscura es un tipo de sustancia con presión negativa, que empezó a dominar recientemente y que es la causa de la aceleración de la expansión del universo.<br/>En esta tesis doctoral presento varios modelos originales propuestos para resolver algunos de los problemas de la cosmología estándar, como posibles extensiones del modelo del Big Bang. Algunos de estos modelos introducen nuevas simetrías y partículas con el fin de explicar la inflación y la energía oscura y/o la materia oscura en una descripción unificada. Uno de los modelos es propuesto para explicar la energía oscura del universo, a través de un nuevo campo escalar que oscila en un potencial.

The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.<br/>According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.<br/>As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe. <br/>In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.<br/>The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, such as the expansion of the universe, the existence of the cosmic microwave background radiation and the relative primordial abundance of light elements. Some of the theoretical predictions have already been confirmed by very precise observations.<br/>According to the standard Big Bang cosmology, the early universe consisted of a very hot and dense plasma that continuously expanded and cooled up to the present, giving place to a series of cosmological phase transitions, where the theories describing the universe in each phase are different. Given that the energies of the early universe were much higher than those reached in terrestrial experiments, the study of the early universe might give us important information about new interactions and new particles, opening new directions for extending the Standard Model of particle physics.<br/>As already mentioned above, during the expansion of the universe, different phase transitions occurred, which left their imprint on the present state of the universe. Observations suggest that during a very early phase transition the universe suffered a stage of accelerated expansion, known as inflation. Although inflation is not included in the standard cosmology, it is able to solve in a simple and elegant manner almost all of the shortcomings related to the standard Big Bang model, and should be taken into account in any possible extension of the theory. Observations also reveal evidence of the existence of two unknown forms of energy, i.e., dark matter and dark energy. Dark matter is a form of non-relativistic and non-baryonic matter, which can only be detected indirectly, by its gravitational interactions with normal matter. Dark energy is a kind of substance with negative pressure, which started to dominate recently and causes the accelerated expansion of the universe. <br/>In this PhD Thesis, I present a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. Some of these models introduce new symmetries and particles in order to explain inflation and dark energy and/or dark matter in a unified description. One of the models is proposed for explaining the dark energy of the universe, by means of a new scalar field oscillating in a potential.