Strong-Field phenomenology in alternative theories of gravitation

Franchini, Nicola (2020) Strong-Field phenomenology in alternative theories of gravitation. PhD thesis, University of Nottingham.

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Assessing the validity of general relativity requires to test its principles and solutions in every possible regime. Up to date, general relativity is in agreement with weak-field tests of gravity and with binary pulsars observations, and it is consistent with the data coming from the detection of gravitational waves emitted by binaries of compact objects. Although general relativity fits the data well, a confrontation with alternative theories would make these results more robust. Such a direct comparison requires predictions for the systems in question in interesting theories beyond general relativity. The first step to compensate for this lack is to understand the physics of black holes and neutron stars within alternative theories of gravity.

This thesis lies in this framework. We analyse the features of compact objects in some selected theories beyond general relativity. The first part is devoted to the aspects of the causality of black holes in theories admitting superluminal perturbations. We study the causal structure of extremal charged black holes in the infrared limit of Ho\v{r}ava gravity, and the propagation of a scalar field around a stationary black hole in Horndeski gravity.

In the rest of the manuscript we discuss the phenomenon of spontaneous scalarization. With this mechanism, one can give rise spontaneously to a scalar field profile around a compact object as a result of a linear tachyonic instability. We analyse the onset of this instability in the context of Horndeski gravity, and its implications to cosmology. Finally, we take a model which breaks the weak equivalence principle, and we use spontaneous scalarization to suppress these violations outside and far away from a neutron star.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Sotiriou, Thomas
Keywords: general relativity, black holes, gravity, mathematical physics
Subjects: Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter
Faculties/Schools: UK Campuses > Faculty of Science > School of Mathematical Sciences
Item ID: 59799
Depositing User: Franchini, Nicola
Date Deposited: 24 Oct 2023 13:24
Last Modified: 24 Oct 2023 13:24

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