Low energy unimodular gravity

• Autores: Sergio González Martín
• Directores de la Tesis: Enrique Álvarez Vázquez (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2018
• Idioma: inglés
• Número de páginas: 135
• Programa de doctorado: Programa de Doctorado en Física Teórica por la Universidad Autónoma de Madrid
• Materias:
  • Física
    • Física teórica
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • It has been known for a century that the theory of General Relativity proposed by Albert Einstein describes accurately gravitational phenomena at low energies. This theory, when considered classically, is capable of reproducing the right results for the tests carried on the Solar system, as well as many other cosmological observations. However, there are several problems when we try to compute quantum effects. Specifically, one of the biggest mysteries of today’s theoretical physics is the so-called cosmological constant problem. This problem is sometimes split in two, on the one hand there is the matter of why it has its particular value (very close to zero but not exactly). On the other hand, quantum corrections to this constant are about 120 orders of magnitude bigger than the observed one.

    Although there are several proposals to solve this problem, some of them by studying the non-perturbative sector of the theory, there is a natural solution to the “second” problem within perturbation theory.

    In this regard, the theory of Unimodular Gravity provides a natural solution to the cosmological constant problem because in this theory the cosmological constant appears as an integration constant at the classical level. Moreover, this theory is compatible with all the current observations. In this work we demonstrate that there are no quantum corrections to first order in perturbation theory to the cosmological constant value, and we argue that this result holds to any loop order as long as the Ward identities are respected.

    Further, since Unimodular Gravity yields the same classical predictions than General Relativity, we look for differences between both theories at the quantum level by adding matter. As part of this study, we show that (for both theories) the beta functions, despite being used as the motivation for proposals such as Asymptotic Safety, lack any physical meaning when matter is coupled to gravity.