Dr Yamashita Yasuho (YITP, Kyoto University)
Recently, a framework of covariant bimetric gravity with no ghost has been established by assuming a restricted form of mass interaction between two metrics derived by de Rham, Gabadadze and Tolley. However, it is not clear why the interaction term takes this specific form and whether the theory can be derived from a more natural setup as a low energy effective theory. In order to improve our understanding of ghost-free bigravity, we consider to reproduce this theory from a braneworld setup as a low energy effective theory. Although this attempt succeeds in the very limited low energy regime, there is a problem: doubly coupled matter. In my talk, I will discuss why doubly coupled matter anticipates difficulties in our attempt and what is our plan to work out this problem.