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Identifier

000395103

Title

Cosmic structures in alternative gravity models

Alternative Title

Κοσμικές δομές σε εναλλακτικά βαρυτικά μοντέλα

Author

Διαλεκτόπουλος, Κωνσταντίνος Φ.

Thesis advisor

Τομαράς, Θεόδωρος

Abstract

The present thesis is a study of cosmic structures in modified gravity models. In particular, we are interested in Brans-Dicke like, scalar-tensor theories in the presence of a positive cosmological constant Λ. We discuss the validity of the no-hair theorem in the context of such theories. We first prove that regular, stationary black-hole solutions exist if and only if the scalar field is constant and the Brans- Dicke parameter, ω, is infinite. These solutions coincide with the General Relativity ones. We also prove perturbatively that, in the absence of the stationary cosmological horizon, black-holes exist with non-trivial ∅−hair. In addition, it is shown that the presence of a stationary cosmological event horizon rules out any regular spherical stationary solution, appropriate for the description of a star. Thus, to describe a star one has to assume deviation from de Sitter asymptotics. Under this assumption generic cosmic structures are studied perturbatively and shown than only for ω > 0 or ω ≤ −5 their predicted maximum sizes are consistent with observations. Finally, we use the perturbative solutions to solve numerically the full (unperturbed) equations and calculate the maximum turnaround radius of different structures, for different values of ω.

Language

English

Subject

Black holes

Brans-Dicke

Scalar-tensor

Βαρύτητα

Γενική σχετικότητα

Μαύρες τρύπες

Τροποποιημένη βαρύτητα

Issue date

2015-07-17