On chromonatural inflation in string theory
  Sourced gravitational waves in chromonatural inflation (CNI) can give rise to
a chiral spectrum of tensor fluctuations that is considerably enhanced relative
to the vacuum fluctuations. If the field content of CNI acts purely as a
spectator (SCNI), the inflationary sector can be consistent with current data
making SCNI very appealing in view of future observations. We investigate the
prospects of embedding SCNI in string theory, in the framework of K\"ahler
inflation in type IIB large volume string compactifications, with a spectator
sector associated with gaugino condensation on multiply magnetised D7-branes.
We first introduce a generalised field theory framework that describes
non-trivial multifield inflation coupled to gauge fields of the form
generically arising in supergravity and string theory. We then use these
results to study numerically and analytically both the background evolution and
the dynamics of cosmological perturbations. We show that a successful
inflationary background evolution with a large enhancement of the gravitational
wave spectrum and a controllable backreaction from the amplified tensor
fluctuations can be achieved by considering suitable values of three parameters
present in our scenario: the magnetic flux, the degree of the condensing gauge
group and the wrapping number of the D7-brane. On the other hand, the required
values for these quantities may present a challenge for its successful
realisation within string theory. We also discuss these challenges and the
model from the viewpoint of the weak gravity conjecture.
