Repetitive Penrose Process in Rotating 4D Einstein-Gauss-Bonnet Black Holes

Abstract

We investigate the repetitive Penrose process for neutral particles in a rotating four-dimensional Einstein--Gauss--Bonnet black hole obtained through the modified Newman--Janis algorithm, developing a nonlinear iterative scheme in which the mass, angular momentum, and irreducible mass are updated after each extraction event. Imposing the triple turning-point condition, we obtain a closed-form solution of the conservation equations for energy, angular momentum, and radial momentum that reduces to the Kerr result in the limit of vanishing coupling. The distinctive feature of this background is that, although the Gauss--Bonnet coupling $\alpha$ is a fixed constant of the action and is not carried by the infalling fragments, the dimensionless coupling $\hat\alpha=\alpha/M^{2}$ grows at every iteration as the mass decreases, so that the effective Gauss--Bonnet correction is self-amplified along the sequence. We find that a larger coupling lowers the extremal spin, contracts the ergosphere, and reduces the number of admissible decays, forbidding the process near the horizon at strong coupling while permitting it at larger decay radii; the termination is controlled throughout by the incident particle. The energy return on investment decreases monotonically with $\hat\alpha$ and the growth of the irreducible mass is suppressed relative to Kerr, whereas the energy utilization efficiency is non-monotonic: below a critical coupling the parameter space exhibits a four-region structure with a bounded window in which the EGB black hole is more efficient than Kerr; this four-region structure collapses into a three-region one above a critical coupling. This coupling-driven reorganization of the efficiency landscape has no analogue in the Kerr, Reissner--Nordstr\"om, Kerr--de~Sitter, accelerating Kerr, or Kerr--Newman cases.