Γενικευμένες Θεωρίες Βαρύτητας με μη-τετριμμένες Ζεύξεις Βαθμωτών Πεδίων

Ντρέκης, Κωνσταντίνος

dc.contributor.author	Ντρέκης, Κωνσταντίνος	el
dc.date.accessioned	2017-09-01T11:03:26Z
dc.date.available	2017-09-01T11:03:26Z
dc.date.issued	2017-09-01
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/45463
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.2722
dc.rights	Default License
dc.subject	Κοσμολογία Βαρύτητα Πληθωρισμός Σκοτεινή Ενέργεια Μελανές Οπές Cosmology Gravity Inflation Dark Energy Black Holes	el
dc.title	Γενικευμένες Θεωρίες Βαρύτητας με μη-τετριμμένες Ζεύξεις Βαθμωτών Πεδίων	el
dc.contributor.department	Physics	el
heal.type	doctoralThesis
heal.classification	Θεωρητική Φυσική	el
heal.language	el
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2017-06-23
heal.abstract	Although General Relativity $($GR$)$ is a very successful theory, passing many tests in our solar system and also being supported by the recent detection of gravitational waves, still remains an incomplete theory. The main goal of this research is the investigation of possible extensions and modifications of gravity in order to obtain a consistent and, if possible, problem-free theory. In particular, we aim to study what kinds of modifications are possible in order to acquire a theoretically justified framework, free of instabilities and pathologies. Since we are entering the $``$gold age$"$ of cosmology, with a huge amount of observational data one should systematically use these data in order to understand how the gravitational interaction works and enlighten issues that until recently were considered as fundamental and purely theoretical. Current observations suggest that the Universe undergoes a phase of accelerated expansion, something that the present theory of GR is not in position to explain. In order to solve problems like the one mentioned, theorists construct models of modified gravity that hope to describe the behavior of the Universe through its history. However, these modern theories have to be put to the test by observations coming from astrophysicists or else they are just pure mathematical models that do not represent realistic scenarios. \qquad A large class of modified gravity theories arise from the consideration of extra degrees of freedom, such as in Brans-Dicke, Galileon, Fab Four and the general Horndeski theories. The Horndeski theory includes scalar fields that are directly and non-minimally coupled to gravity. Constructing such models, implementing them into various cosmological scenarios, testing their validity through observation and constraining their parameter space is the main purpose of this research. The aforementioned objective consists of suitably generalizing and modifying the gravitational action, using non-minimally coupled scalar fields, requiring absence of various instabilities at the zeroth as well as the perturbative level and retrieving GR at a particular limit. By extracting the gravitational field equations one can obtain the corresponding solutions and formulate the various observables as functions of the parameters of the theory. One can then use observational data to examine whether these solutions are in agreement with the current knowledge of numerous cosmological aspects. Such an analysis can concern issues arising at the inflationary paradigm, the formation and properties of black holes and the ongoing state of our universe, the accelerated expansion. \qquad Some of the already published results of this Ph.D. thesis include the formulation of a suppression mechanism for the particle production during the inflation scenario, the breaking of the degeneracy of inflationary models through the measurement of the reheating temperature $($during the reheating phase$)$ after inflation, the gravitational collapse of a scalar field to the formation of a black hole and a unification scenario for the Dark Matter-Dark Energy components.	en
heal.advisorName	Κουτσούμπας, Γεώργιος	el
heal.committeeMemberName	Αναγνωστόπουλος, Κωνσταντίνος	el
heal.committeeMemberName	Ήργες, Νικόλαος	el
heal.committeeMemberName	Ζουπάνος, Γεώργιος	el
heal.committeeMemberName	Κεχαγιάς, Αλέξανδρος	el
heal.committeeMemberName	Κουτσούμπας, Γεώργιος	el
heal.committeeMemberName	Παπαντωνόπουλος, Ελευθέριος	el
heal.committeeMemberName	Φαράκος, Κωνσταντίνος	el
heal.academicPublisher	Σχολή Εφαρμοσμένων Μαθηματικών και Φυσικών Επιστημών	el
heal.academicPublisherID	ntua
heal.numberOfPages	151
heal.fullTextAvailability	true