Aspects of Black Hole Physics: Scalar Sources, Holography and Gravitational Wave Emission

We investigate several aspects of black hole physics. First, we consider models of gravity minimally coupled to scalar fields. We derive a new class of asymptotically flat black holes sourced by a non-trivial asymptotically massless scalar field; we discuss their relationship with known solutions and standard no-hair theorems and their thermodynamics. We derive exact neutral and charged brane solutions sourced by a scalar field with vanishing potential, which are conformal to the Lifshitz spacetime; we discuss the symmetries and their holographic application for hyperscaling violation; we also give a quite general classification of brane solutions sourced by scalar fields useful for holographic applications. We study an inflationary model inspired by the domain wall/cosmology correspondence in which inflation is driven by a scalar with a two-exponential potential; we derive its phenomenological consequences in the slow-roll approximation and compare its predictions with the Planck 2015 data. Second, we investigate ultra-compact astrophysical objects which can act as black hole mimickers, in particular boson stars and wormholes. We discuss the existence and the stability of boson stars in higher dimensions and boson stars built with multiple scalars. We compute tidal Love numbers for various mimickers and discuss how to distinguish black holes from their possible mimickers with gravitational-wave data. We study the gravitational radiation emitted by a particle falling into an exotic compact object and show that the initial ringdown signal cannot be use distinguish between a black hole and a black hole mimicker.