Regular black holes in de Sitter universe: Scalar field perturbations and quasinormal modes

The purpose of this paper is to study quasinormal modes (QNMs) of a regular black hole with a cosmological constant due to scalar perturbations. A detailed study of QNMs frequencies for the massless scalar field was done by varying the parameters of the theory such as mass, magnetic charge, cosmological constant and the spherical harmonic index. We have employed the sixth-order WKB approximation to compute the QNMs frequencies. We have also proved analytically that the l = 0 mode for the massless field reaches a constant value at late times. We have approximated the near-extreme regular-de Sitter (dS) black hole potential with the Poschl-Teller potential to obtain exact frequencies. The null geodesics of the regular-de Sitter black hole is employed to describe the QNMs frequencies at the eikonal limit (l >> 1).