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Q-ball superradiance: Analytical approach

Guo-Dong Zhang1,*, Shuang-Yong Zhou1,2,†, and Meng-Fan Zhu3,‡

  • *Contact author: guodongz@mail.ustc.edu.cn
  • †Contact author: zhoushy@ustc.edu.cn
  • ‡Contact author: skyer@mail.ustc.edu.cn
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Phys. Rev. D 113, 056020 – Published 24 March, 2026

DOI: https://doi.org/10.1103/rwj6-nsl8

Abstract

It was recently discovered that waves scattering off a Q ball can extract energy from it. We present an analytical treatment of this process by adopting a multistep function approximation for the background field, which yields perturbative solutions expressed in terms of Bessel functions. For thin-wall Q balls, the amplification factors reduce to simple sinusoidal functions, which explains the multipeak structure of the spectrum and identifies the physical quantities that determine it. For instance, at high frequencies, the peak spacing is simply the inverse of the Q-ball size. The analytical solution further enables us to delineate the full range of possible amplification factors. For general Q balls, this analytical framework also substantially improves the efficiency of evaluating the amplification factors.

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Phys. Rev. D 113, 056020– Published 24 March, 2026
  • Received 10 November 2025
  • Accepted 23 February 2026
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