Inflation: scopes and cautions in model building

CMB observations have been testing inflation at scales ranging from a few Mpc to Gpc, delivering stringent limits on the amplitudes of inflationary perturbations and their scale-dependence and pointing to an effectively single field behaviour. However, at intermediate and small scales, closer to the end of inflation, inflationary dynamics can dramatically deviate from slow-roll exhibiting a rich phenomenology for scalar and tensor fluctuations. Intriguing examples include the possibility of a large primordial gravitational wave (GW) spectrum and the existence of several mechanisms for primordial black holes (PBH) production. Inflation models originating from high energy theories often consist of multiple fields. Remarkably, there is a large range of couplings of the inflaton with other sectors that can lead to signatures in primordial perturbations. These can can be probed by current and upcoming GW surveys. In this talk, I will present two such theoretically motivated models, highlighting their dynamics at small scales.