  We consider the effects of backreaction on axion-SU(2) dynamics during
inflation. We use the linear evolution equations for the gauge field modes and
compute their backreaction on the background quantities numerically using the
Hartree approximation. We show that the spectator chromo-natural inflation
attractor is unstable when back-reaction becomes important. Working within the
constraints of the linear mode equations, we find a new dynamical attractor
solution for the axion field and the vacuum expectation value of the gauge
field, where the latter has an opposite sign with respect to the chromo-natural
inflation solution. Our findings are of particular interest to the
phenomenology of axion-SU(2) inflation, as they demonstrate the instability of
the usual trajectory due to large backreaction effects. The viable parameter
space of the model becomes significantly altered, provided future non-Abelian
lattice simulations confirm the existence of the new dynamical attractor. In
addition, the backreaction effects lead to characteristic oscillatory features
in the primordial gravitational wave background that are potentially detectable
with upcoming gravitational wave detectors.
