In this work, we perform the first numerical study of strong scalar backreaction in spectator chromo-natural inflation in the case where the spectator sector decays during inflation. The tachyonic instability in scalar fluctuations, activated as the system crosses the $m_Q=\sqrt{2}$ threshold, amplifies perturbations and may significantly alter the background dynamics. The strong scalar backreaction regime introduces an effective quartic term in the potential for the gauge field background that rapidly drives it to zero, accelerating the axion-gauge system decay. We take a first step toward characterizing the dynamics of this scenario by studying the fluctuations at the linearized level, thus providing a necessary benchmark for future nonperturbative analyses. We describe the dynamics of such decay and derive the gravitational wave spectrum for a set of benchmark parameters. Interestingly, the signal may peak at interferometer scales and lie within Laser Interferometer Space Antenna’s projected sensitivity.

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• Cosmology
• Gravitational wave sources
• Gravitational waves
• Inflation
• Astrophysical & cosmological simulations
• Numerical simulations in gravitation & astrophysics