Speaker
Description
Q-balls are non-topological solitons and promising dark matter candidates. Their potential astrophysical signatures motivate a thorough understanding of their wave scattering properties. The central contribution of this work is an analytical elucidation of the multi-peak structure in Q-ball superradiance. By discretizing the background Q-ball and applying resummation techniques, the perturbative solution is expressed as a linear combination of Bessel functions. In the thin-wall, large-radius limit, we obtain closed-form analytical expressions for the scattering amplitude and amplification factor. These expressions explicitly reveal how the multi-peak spectrum is modulated by the Q-ball size and incident wave frequency. The result holds for arbitrary potentials, confirms that the amplification factor remains finite near the mass gap, and yields stronger theoretical constraints when incorporated into the amplification bounds. Our analytical predictions are validated against full numerical calculations.
In addition to this analytical work, we also investigate superradiance in two other scenarios. First, for \textbf{spinning Q-balls} in (2+1) and (3+1) dimensions, we obtain amplification factor spectra for energy, angular momentum, and their fluxes, and derive constraints on single ingoing modes using particle number conservation. Second, in the \textbf{Friedberg–Lee–Sirlin (FLS) model} — which couples a complex scalar field with a real scalar field — we find that perturbative scattering waves involve three coupled modes. Using relaxation iteration methods, we show that the mass ratio of the two fields significantly affects the amplification factors, and that larger solitons produce more peaks in the spectra.
Collectively, this work provides deep analytical insight into the origin of superradiant peaks, alongside systematic numerical explorations of spinning Q-balls and the FLS model, offering a controllable theoretical framework for understanding and potentially detecting Q-ball superradiance in the context of dark matter.