Stochastic gravitational wave backgrounds from primordial black holes

The field of gravitational waves has made a huge progress over the last decade, especially since their first detection by LIGO in September 2015. In this defense, I will give an overview of some of the research lines where this progress is more tangible, all of them related in some way to the stochastic gravitational wave background or primordial black holes. First, gravitational waves and the stochastic gravitational wave background will be introduced, together with some data analysis works using LIGO-Virgo-KAGRA data. We will then see how to set constraints to this background below the nano-Hertz by using astrometric data from astronomical surveys such as Gaia. Finally, we will study some of the phenomena related to hyperbolic encounters and primordial black holes, particularly the stochastic gravitational wave backgrounds they produce and the spin induction effect which arises in these interactions.