Low-Energy Effective Field Theory for Chromo-Natural Inflation
  Chromo-natural inflation is a novel model of inflation which relies on the
existence of non-abelian gauge fields interacting with an axion. In its
simplest realization, an SU(2) gauge field is assumed to begin inflation in a
rotationally invariant VEV. The dynamics of the gauge fields significantly
modifies the equations of motion for the axion, providing an additional damping
term that supports slow-roll inflation, without the need to fine tune the axion
decay constant. We demonstrate that in an appropriate slow-roll limit it is
possible to integrate out the massive gauge field fluctuations whilst still
maintaining the nontrivial modifications of the gauge field to the axion. In
this slow-roll limit, chromo-natural inflation is exactly equivalent to a
single scalar field effective theory with a non-minimal kinetic term, i.e. a
P(X,\chi) model. This occurs through a precise analogue of the gelaton
mechanism, whereby heavy fields can have unsuppressed effects on the light
field dynamics without contradicting decoupling. The additional damping effect
of the gauge fields can be completely captured by the non-minimal kinetic term
of the single scalar field effective theory. We utilize the single scalar field
effective theory to infer the power spectrum and non-gaussianities in
chromo-natural inflation and confirm that the mass squared of all the gauge
field fluctuations is sufficiently large and positive that they completely
decouple during inflation. These results confirm that chromo-natural inflation
is a viable, stable and compelling model for the generation of inflationary
perturbations.
