Thesis

Challenging theories of gravitation: dark matter, compact objects and gravitational waves

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• Domains:

  General Relativity | Astrophysics

• Supervisor:

  Vitor Cardoso

• Co-Supervisor:

  Leonardo Gualtieri

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Instituto Superior Técnico

• Abstract:

  On September 14, 2015 the two LIGO interferometers have detected for the first time the gravitational wave signal emitted during the coalescence of a binary black hole system. This detection provides the first direct evidence of the existence of black holes and of the existence of BH binaries. It also allows to test, for the first time, gravity in the strong-field regime and close to horizons. This proposal aims at studying how possible modifications of general relativity would affect the gravitational wave signal emitted by astrophysical sources, in order to constrain such modifications. I shall consider some of the simplest and most interesting modifications of GR: (i) scalar-tensor theories, in which the tensor field which mediates gravity is (non-minimally) coupled to a scalar field, and (ii) theories in which the Einstein-Hilbert action includes higher-order curvature invariants coupled to scalar fields, such as Einstein-Dilaton-Gauss-Bonnet gravity and Chern- Simons gravity. The main strong-gravity astrophysical processes I want to study are: - the so-called "spontaneous scalarization" phenomena, which are non-trivial scalar field configurations associated to neutron stars, in the context of scalar-tensor theories; I have studied this process in my master thesis, focussing on the case of massive scalar fields; next step is the modeling of the gravitational wave signal, and the study of its detectabilityl - the excitation of the quasi-normal modes of oscillations of black holes in quadratic gravity theories; these modes are excited in the final part of a binary black hole coalescence (as predicted by numerical simulations, and confirmed in the LIGO detection), and carry the imprint of the underlying gravity theory in the strong-field, high-curvature regime.