A Way of Decoupling the Gravitational Bulk Field Equations of Regular Braneworld Black Holes to Suppress the Bulk Singularities

Abstract

The authors provide a methodology for decoupling the bulk gravitational field equations of braneworld black holes (BHs) to suppress the bulk singularities. Thus, a regular braneworld BH setup is provided. To achieve this, a minimal geometric deformation is applied with respect to a coupling constant $\alpha$ to the $4D$ Minkowski spacetime embedded in an extra dimension. This results in a gravitational decoupling into a system $A$ with equations of motion of order ${\alpha }^0$ and a system $B$, related to the so-called Quasi–Einstein equations of order $\alpha$. This methodology allows for the construction of a regular geometry everywhere. The necessary constraints for eliminating singularities is outlined and provide a recipe for solving the equations of motion. Both the warp factor, the scalar field, and the potential obtained are smooth and free from Dirac delta singularities. A control parameter is introduced such that, in the limit $b\to 0$, the Randall–Sundrum setup is recovered, resulting in a transition from a thick brane to a thin brane. The asymptotic behavior of the curvature invariant ${\lim }_{y\to \pm \infty }{R}_{5D}(r,y)$ is positive near the de Sitter core (for small $r$), asymptotically negative for finite $r>r_{\ast }$, and asymptotically flat at the $4D$ boundary as $r\to \infty$. Although this work aims to suppress bulk singularities, it is expected that our methodology may be useful for future investigations related to the embedding of gravitational objects within other braneworld contexts.