Gravitational waves detectable in laser interferometers from axion-SU(2)
  inflation
  Chromo-natural inflation (CNI) is an inflationary model where an axion
coupled with SU$(2)$ gauge fields acts as the inflaton. In CNI, the gauge
fields have nonzero vacuum expectation values (VEVs), which results in the
enhancement of gravitational waves (GWs). The original CNI is ruled out by the
Planck observations due to the overproduction of GWs. In this work, we consider
an inflationary model where the gauge fields acquire nonzero VEVs after the CMB
modes exit the horizon. Moreover, we add to the model another field that
dominates the universe and drives inflation after the axion starts to oscillate
and the gauge field VEVs vanish. By performing numerical simulations, we find a
parameter space where the enhanced GWs do not violate the CMB constraints and
can be detected by the future GWs observations such as LISA, BBO, and ET.
