Yasuho Yamashita (Yukawa Institute for Theoritical Physics, Japan)
Recently the ghost-free bigravity, the gravitational theory which contains two metrics interacting each other, is constructed by tuning the interaction terms to remove Boulware-Deser ghost. Using this model, we can realize the late-time cosmic accelerating expansion and the gravitational wave has a charasteristic feature. However, we have no idea what is the mechanism which tunes the interaction terms to the specific ones derived by the ghost-free condition technically. Therefore, we tried to derive the ghost-free bigravity as an low-energy effective theory of DGP 2-brane model. I will talk about the attempt to obtain a bigravity model by solving the bulk metric with the gradient expansion and how this bigravity model behaves compared with the ghost-free bigravity.