Quasinormal modes of spherically symmetric black hole with cosmological constant and global monopole in bumblebee gravity

This paper studies the scalar, electromagnetic field and Dirac field perturbations of a spherically symmetric black hole within the framework of the Einstein-bumblebee gravity model with a global monopole and cosmological constant. We investigate the effective potentials, greybody factors and quasinormal modes (QNMs) by applying the Klein-Gordon equation, electromagnetic field equation and Dirac equation expressed in the Newman-Penrose (NP) formalism. Using the general method of rigorous bound, the greybody factors of scalar, electromagnetic and Dirac field are derived. Applying the sixth order WKB approximation and Padé approximation, the QNM frequencies are derived. We also discuss the impact of global monopole η, cosmological constant Λ and Lorentz violation parameter L to the effective potential, greybody factor and QNMs. Increasing the parameter η prevents the rise of effective potential for both Schwarzschild-de Sitter (SdS)-like and Schwarzschild-Anti de Sitter (SAdS)-like black holes with global monopole and consequently increases the greybody factors. However, decreasing the parameter L reduces the rise of effective potential for the SAdS-like black hole with global monopole and it increases the greybody factor but increasing the parameter L has the opposite effect for the SdS-like black hole with global monopole. It is also shown that the shadow radius increases with increasing the parameter η for both the SdS and SAdS-like black holes. Increasing the value of L tends to decrease the shadow radius for the SdS-like black hole but it has the opposite effect in the SAdS-like black hole. A careful studying is being carried out to investigate how the absorption cross-section gets affected when the parameter L appears into the picture.