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arXiv · 2606.29704

Quasibound states of a charged Dirac field around regular black holes

Shao-Jun Zhang
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Abstract

Charged regular black holes can respond differently from Reissner--Nordstr\"om (RN) black holes to charged scalar perturbations, raising the question of whether their inner geometry also leaves a distinct imprint on fermionic fields, for which classical superradiant amplification is absent. We address this question by studying quasibound states of a massive charged Dirac field on the Ay\'on-Beato--Garc\'{\i}a (ABG) regular black-hole background. We derive the separated radial equations and the far-field trapping condition $M\mu^2-qQ\omega_R>0$, compute the complex spectrum by two-sided shooting and matching, and independently identify the long-lived modes in time-domain evolutions. The identical Newtonian and Coulomb tails of ABG and RN produce the same leading hydrogenic spectrum, so their real frequencies differ only through subleading corrections and full radial matching. The damping rates are much more sensitive to the inner geometry: changes in the near-horizon potential barrier suppress or enhance the leakage of the fermionic cloud into the horizon, and some ABG modes live more than an order of magnitude longer than their RN counterparts despite having nearly identical real frequencies. All modes found in the explored parameter range remain damped. Thus the regular geometry changes the lifetime, rather than the leading binding energy, of the fermionic cloud without generating a Dirac superradiant instability.

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Shao-Jun Zhang. 2026-06-29. Quasibound states of a charged Dirac field around regular black holes. https://arxiv.org/abs/2606.29704

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