Stability of Einstein static state universe in the spatially flat branemodels

With the assumption that a perfect fluid with a constant equation of state is the only energy component on the brane, we study the stability of Einstein static state solution under homogeneous and inhomogeneous scalar perturbations in both spatially flat Randall–Sundrum (RS) and Shtanov–Sahni (SS) braneworlds. We find that if the perfect fluid has a phantom-like property and the “Weyl fluid” originating from the projection of the bulk Weyl tensor onto the brane behaves like a radiation with positive energy density, the Einstein static state solution is stable in the SS braneworld, but unstable in the RS one. Furthermore, we demonstrate that the static state solution is also stable in the bulk with a timelike extra dimension. Thus, in the model where the extra dimension is timelike, our universe can stay at the Einstein static state past-eternally, which means that the big bang singularity might be resolved successfully by an emergent scenario