Grey-body factors and absorption cross-sections of scalar and Dirac fields in the vicinity of dilaton-de Sitter black hole

We investigate the propagation of a massive scalar field and a massless Dirac field in the geometry of a dilaton–de Sitter black hole. Starting from the covariant perturbation equations, we present the corresponding effective potentials and analyze their dependence on the dilaton charge, field mass, and cosmological constant. Using the WKB approximation, we compute the grey-body factors and study the associated absorption cross-sections. The results show that increasing the field mass or dilaton charge raises the effective potential barrier, leading to a suppression of transmission at low frequencies, while a larger cosmological constant lowers the barrier and enhances transmission. The partial absorption cross-sections for different multipole numbers display the expected oscillatory structure, with the lowest multipoles dominating at small frequencies. After summation over multipoles, the oscillations average out and the total cross-section interpolates between strong suppression in the infrared regime and the geometric capture limit at high frequencies. These findings provide a systematic description of scattering and absorption properties of dilaton–de Sitter black holes for both scalar and fermionic perturbations.

💡 Research Summary

This paper investigates the scattering and absorption of massive scalar fields and massless Dirac fields in the background of a dilaton–de Sitter (dilaton‑de Sitter) black hole. The authors begin by reviewing the low‑energy string‑inspired action that includes a dilaton field Φ with a potential V(Φ) = Λ₃(e^{2(Φ−Φ₀)} + e^{-2(Φ−Φ₀)}) + 4Λ₃, a Maxwell term coupled as e^{-2Φ}F², and a positive cosmological constant Λ. Solving the field equations yields the metric
ds² = –f(r) dt² + dr²/f(r) + R²(r)(dθ² + sin²θ dφ²)
with f(r) = 1 – 2M/r – Λ r³ (r – 2Q) and R²(r) = r² – 2Qr, where Q is the dilaton charge and M is set to unity.

The dynamics of a massive scalar φ (mass μ) and a massless Dirac spinor Υ are governed respectively by the covariant Klein‑Gordon equation (∇² – μ²)φ = 0 and the Dirac equation γ^α(∂α – Γ_α)Υ = 0. After separating variables and introducing a suitable radial function Ψ, both equations reduce to a Schrödinger‑like form
d²Ψ/dr*² +