Gravitational waves (GWs) have a great potential to probe cosmology. We review early universe sources that can lead to cosmological backgrounds of GWs. We begin by presenting proper definitions of GWs in flat space-time and in a cosmological setting …
Black holes (BHs) in general relativity (GR) are very simple objects. This property, that goes under the name of `no-hair', has been refined in the last few decades and admits several versions. The simplicity of BHs makes them ideal testbeds of …
One century after its formulation, Einstein's general relativity (GR) has made remarkable predictions and turned out to be compatible with all experimental tests. Most of these tests probe the theory in the weak-field regime, and there are …