Efficient self-resonance instability from axions

Abstract

It was recently shown that a coherent oscillation of an axion can cause an efficient parametric resonance, leading to a prominent emission of the gravitational waves (GWs). In this paper, conducting the Floquet analysis, we investigate the parametric resonance instability, which potentially triggers the emission of the GWs from axions. Such a resonance instability takes place, when the time evolution of the background field significantly deviates from the harmonic oscillation. Therefore, the resonance instability cannot be described by the Mathieu equation, whose stability/instability chart is well known. In this paper, introducing an explicitly calculable parameter $\tilde{q}$, which can be used to classify different types of the parametric resonance described by the general Hill's equation, we investigate the stability/instability chart for the general Hill's equation. This can also apply to the case where the background oscillation is anharmonic. We show that the flapping resonance instability, which takes place for $\tilde{q}=O(1)$, typically leads to the most significant growth of the inhomogeneous modes among the self-resonance instability. We also investigate whether the flapping resonance takes place for the cosine potential or not.

23 pages, 13 figures

References in corpus (10)

• Nonperturbative Dynamics Of Reheating After Inflation: A Review
• A Gravitational Wave Background from Reheating after Hybrid Inflation
• Gravitational Wave Production At The End Of Inflation
• A stochastic background of gravitational waves from hybrid preheating
• Flat-top oscillons in an expanding universe
• Gravitational perturbations from oscillons and transients after inflation
• Decay of I-ball/Oscillon in Classical Field Theory
• Pure Natural Inflation
• Notes on natural inflation
• Analytical study of the parametric instability of an oscillating scalar field in an expanding universe