Thesis

Foundations of extended theories of gravity and applications

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

  General Relativity | Cosmology

• Supervisor:

  Francisco Lobo

• Co-Supervisor:

• Institution:

  Faculdade de Ciências - Universidade de Lisboa

• Host Institution:

  Universidade de Lisboa

• Abstract:

  Modern physics is moving through very deep and fundamental questions regarding the nature of the physical realm. Einstein´s theory of general relativity opened the door for a dynamical role of spacetime geometry in physics. Indeed, it is strongly believed that there is a deep relation between the geometry of spacetime and physical fields on a fundamental level and, in general, it is assumed that at some high energy scale there is a mathematical description that unifies different dynamical interactions. Historically, new ideas on spacetime provided new insights into physics by revealing new phenomena and/or improving our geometrical methods crucial for modern physics. In this context, extended theories of gravity have a great relevance. One possibility is to change the geometrical side of the gravitational field equations and include other geometrical entities previously unconsidered. In fact, the exploration of geometries beyond the (pseudo) Riemannian allows us to introduce torsion and search for its physical relevance in the construction of alternative theories of gravity and unified modern field theories. This work will address fundamental research on extended theories of gravity and its astrophysical and cosmological applications, including gravitational waves. Some of the topics to cover, such as f(R) theories, gravity with torsion, the applications of these to cosmic acceleration and the dark matter problem, gravitational waves and also the coupling of gravity and electromagnetism, are areas of active research from the theoretical side that have become gradually more significant in observational astrophysics and cosmology. The possibility of testing these theories experimentally will be extensively explored. The study of geons with extended theories of gravity has also recently revealed to be a very rich domain of applicability of these theories in connection to the coupling of gravity and electromagnetism and astrophysical and cosmological issues such as black hole remnants and primordial black holes. Moving to the quantum domain, these geons might provide a deeper understanding of the relation between the local topological nature of the electromagnetic-gravitational (spacetime) vacuum and the quantum gravity challenge. This work will explore new horizons in the production of coupled gravitational-electromagnetic waves and their detection. These can have different sources since most astrophysical objects with a strong gravitational field also have a very strong electromagnetic field. We will study the perturbations of the gravitational-electromagnetic environment of geons and address several astrophysical and observational implications. All these issues open new windows for the physics of gravitational waves (in Einstein gravity and beyond) but also to the active research on the experimental tests of modified theories of gravity and spacetime torsion.