Daisuke Yoshida (Tokyo Institute of Technology, Japan)
We investigate perturbations of a class of time-dependent spherically symmetric solutions in bi-gravity, which includes both FLRW space time and Schwarzschild de Sitter space time. We consider the solutions which can be obtained only when the parameters of bi-gravity satisfy a special relation. In this case, It is known that the equation of motion for spherically symmetric space time reduces to the Einstein equation with an effective cosmological constant. We find this property is true even in the level of general perturbation, namely, the equations of motion of perturbations become the perturbed Einstein equation. This result shows, even if any observation about the perturbation of spherically symmetric space time coincide with the prediction of General Relativity, we can not dissmiss the theoy of bi-gravity.