Low-frequency gravitational waves from massive black holes: implications for fundamental physics and astrophysics*

The observation of compact binary mergers by the LIGO/Virgo collaboration marked the dawn of a new era in astronomy. LISA will fulfill this vision by opening a new observational window at low frequencies. The gravitational radiation emitted by compact binaries in the LISA band encodes important information on their astrophysical formation mechanism. Furthermore, compact objects - whether in isolation or in binaries - are excellent astrophysical laboratories to probe our understanding of high-energy physics and strong-field gravity. I will discuss how LISA can further our understanding of the formation and evolution of compact binaries, test gravity in the strong field regime, and look for smoking guns of new physics.