Quasi-resonances in the vicinity of Einstein-Maxwell-dilaton black hole

Abstract

We study massive scalar quasinormal spectra of charged Einstein--Maxwell--dilaton black holes by combining high-order WKB--Pad\'e calculations with time-domain evolution. The two approaches show close agreement in the regime where both methods are reliable, allowing controlled tracking of spectral trends across different charges and dilaton couplings. We find that increasing scalar-field mass can strongly suppress damping for several branches, signaling an approach to quasi-resonant, very long-lived oscillations. Although WKB is not expected to determine modes extremely close to the real-frequency axis with high precision, the onset of this regime is clear and appears for multiple dilaton couplings, with additional near-resonant behavior in lower-multipole sectors. The dilaton-induced shifts are substantially larger than the estimated numerical uncertainty, indicating that quasi-resonances are a robust physical signature relevant for ringdown spectroscopy in scalar-extended gravity.