New effective theories of gravitation and their phenomenological consequences

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dc.contributor.advisorDe La Cruz-Dombriz, Alvaro
dc.contributor.advisorMazumdar, Anupam
dc.contributor.authorMaldonado Torralba, Francisco José
dc.date.accessioned2021-01-15T09:53:38Z
dc.date.available2021-01-15T09:53:38Z
dc.date.issued2020
dc.description.abstractThe objective of this Thesis is to explore Poincaré Gauge theories of gravity and expose some contributions to this field, which are detailed below. Moreover, a novel ultraviolet non-local extension of this theory shall be provided, and it will be shown that it can be ghost- and singularity-free at the linear level. First, we introduce some fundamentals of differential geometry, base of any gravitational theory. We then establish that the affine structure and the metric of the spacetime are not generally related, and that there is no physical reason to impose a certain affine connection to the gravitational theory. We review the importance of gauge symmetries in Physics and construct the quadratic Lagrangian of Poincaré Gauge gravity by requiring that the gravitational theorymust be invariant under local Poincaré transformations. We study the stability of the quadratic Poincaré Gauge Lagrangian, and prove that only the two scalar degrees of freedom (one scalar and one pseudo-scalar) can propagate without introducing pathologies. We provide extensive details on the scalar, pseudo-scalar, and bi-scalar theories. Moreover, we suggest how to extend the quadratic Poincaré Gauge Lagrangian so that more modes can propagate safely. We then proceed to explore some interesting phenomenology of Poincaré Gauge theories. Herein, we calculate how fermionic particles move in spacetimes endowed with a nonsymmetric connection at first order in the WKB approximation. Afterwards, we use this result in a particular black-hole solution of Poincaré Gauge gravity, showing that measurable differences between the trajectories of a fermion and a boson can be observed. Motivated by this fact, we studied the singularity theorems in theories with torsion, to see if this non-geodesical behaviour can lead to the avoidance of singularities. Nevertheless, we prove that this is not possible provided that the conditions for the appearance of black holes of any co-dimension are met. In order to see which kind Black Hole solutions we can expect in Poincaré Gauge theories, we study Birkhoff and no-hair theorems under physically relevant conditions. Finally, we propose an ultraviolet extension of Poincaré Gauge theories by introducing non-local (infinite derivatives) terms into the action, which can ameliorate the singular behaviour at large energies. We find solutions of this theory at the linear level, and prove that such solutions are ghost- and singularity-free. We also find new features that are not present in metric Infinite Derivative Gravity.
dc.identifier.apacitationMaldonado Torralba, F. J. (2020). <i>New effective theories of gravitation and their phenomenological consequences</i>. (Doctoral Thesis). University of Cape Town. Retrieved from http://hdl.handle.net/11427/32548en_ZA
dc.identifier.chicagocitationMaldonado Torralba, Francisco José. <i>"New effective theories of gravitation and their phenomenological consequences."</i> Doctoral Thesis., University of Cape Town, 2020. http://hdl.handle.net/11427/32548en_ZA
dc.identifier.citationMaldonado Torralba, F.J. 2020. New effective theories of gravitation and their phenomenological consequences. Doctoral Thesis. University of Cape Town. http://hdl.handle.net/11427/32548en_ZA
dc.identifier.ris TY - Doctoral Thesis AU - Maldonado Torralba, Francisco José AB - The objective of this Thesis is to explore Poincaré Gauge theories of gravity and expose some contributions to this field, which are detailed below. Moreover, a novel ultraviolet non-local extension of this theory shall be provided, and it will be shown that it can be ghost- and singularity-free at the linear level. First, we introduce some fundamentals of differential geometry, base of any gravitational theory. We then establish that the affine structure and the metric of the spacetime are not generally related, and that there is no physical reason to impose a certain affine connection to the gravitational theory. We review the importance of gauge symmetries in Physics and construct the quadratic Lagrangian of Poincaré Gauge gravity by requiring that the gravitational theorymust be invariant under local Poincaré transformations. We study the stability of the quadratic Poincaré Gauge Lagrangian, and prove that only the two scalar degrees of freedom (one scalar and one pseudo-scalar) can propagate without introducing pathologies. We provide extensive details on the scalar, pseudo-scalar, and bi-scalar theories. Moreover, we suggest how to extend the quadratic Poincaré Gauge Lagrangian so that more modes can propagate safely. We then proceed to explore some interesting phenomenology of Poincaré Gauge theories. Herein, we calculate how fermionic particles move in spacetimes endowed with a nonsymmetric connection at first order in the WKB approximation. Afterwards, we use this result in a particular black-hole solution of Poincaré Gauge gravity, showing that measurable differences between the trajectories of a fermion and a boson can be observed. Motivated by this fact, we studied the singularity theorems in theories with torsion, to see if this non-geodesical behaviour can lead to the avoidance of singularities. Nevertheless, we prove that this is not possible provided that the conditions for the appearance of black holes of any co-dimension are met. In order to see which kind Black Hole solutions we can expect in Poincaré Gauge theories, we study Birkhoff and no-hair theorems under physically relevant conditions. Finally, we propose an ultraviolet extension of Poincaré Gauge theories by introducing non-local (infinite derivatives) terms into the action, which can ameliorate the singular behaviour at large energies. We find solutions of this theory at the linear level, and prove that such solutions are ghost- and singularity-free. We also find new features that are not present in metric Infinite Derivative Gravity. DA - 2020 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PY - 2020 T1 - New effective theories of gravitation and their phenomenological consequences TI - New effective theories of gravitation and their phenomenological consequences UR - http://hdl.handle.net/11427/32548 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/32548
dc.identifier.vancouvercitationMaldonado Torralba FJ. New effective theories of gravitation and their phenomenological consequences. [Doctoral Thesis]. University of Cape Town, 2020 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/32548en_ZA
dc.language.isoeng
dc.publisherUniversity of Cape Town
dc.publisher.departmentDepartment of Mathematics and Applied Mathematics
dc.publisher.facultyFaculty of Science
dc.subject.otherCosmology
dc.subject.otherGravitation
dc.subject.otherPoincaré Gauge theories
dc.titleNew effective theories of gravitation and their phenomenological consequences
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhD
uct.type.publicationResearch
uct.type.resourceDoctoral Thesis
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