Bi-gravity from DGP Two-brane Model – Yasuho Yamashita

Date: Wed. October 28th, 2015, 12:30 pm-1:30 pm
Location: Rockefeller 221

We discuss whether or not bigravity theory can be embedded into the braneworld setup. As a candidate, we consider Dvali-Gabadadze-Porrati two-brane model. We will show that we can construct a ghost free model whose low energy spectrum is composed of a massless graviton and a massive graviton with a small mass, fixing the brane separation with the Goldberger-Wise radion stabilization. We also show that there is two branches: the normal branch is stable and the self-accelerating branch is inevitably unstable, and discuss the condition for the normal branch. Next, we consider DGP two-brane model without the radion stabilization to discuss how the ghost free bigravity coupled with a single scalar field can be derived from a braneworld setup. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. The obtained effective theory is shown to be ghost free as expected. We also find that the radion remains as a massless scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.