Sharp turns in axion monodromy: primordial black holes and gravitational
  waves
  Large and sharp turns in multifield inflation can lead to a very rich
phenomenology, but are difficult to realise in supergravity, and typically
require large field space curvatures. In this work, we present a mechanism to
realise multiple sharp turns, and therefore strong non-geodesic trajectories,
from transient violations of slow-roll without the requirement of large field
space curvatures in supergravity inflation. Such turning rates can strongly
source the adiabatic fluctuations, resulting in an enhanced scalar power
spectrum with a large peak amplitude. If the growth of the scalar power
spectrum is large enough, primordial black holes can be produced in abundance.
Moreover, these large scalar fluctuations induce a characteristic large
spectrum of gravitational waves for a wide range of frequencies. We illustrate
this mechanism in a supergravity model of axion monodromy. The model can
sustain inflation for around 60 e-folds satisfying the cosmic microwave
background constraints at large scales, while leading to considerable
production of very light primordial black holes and large gravitational wave
spectra, potentially detectable by multiple upcoming gravitational wave
surveys.
