Strong Coupling vs. 4-D Locality in Induced Gravity

TL;DR

The paper studies a UV-regularized brane-induced gravity model and shows it can avoid the strong coupling and ghost problems that plague DGP at cubic order. Using a scalar toy model and a detailed mode analysis, it demonstrates that the 4-D dynamics on the brane can be induced by bulk physics without a separate brane kinetic term, with a crossover scale $L=\epsilon\Delta$ governing 4-D vs 5-D propagation. The scalar sector acquires a healthy kinetic term through mixing, leading to a strong coupling scale $\Lambda_3=(M_P M_*^2)^{1/3}$ well above the UV cutoff $M_*$, suggesting perturbation theory remains controlled. Nevertheless, the regularization introduces nonlocality in the 4-D metric and potential all-order gauge issues, requiring further checks for full consistency.

Abstract

We re-examine the problem of strong coupling in a regularized version of DGP (or ``brane-induced'') gravity. We find that the regularization of ref. hep-th/0304148 differs from DGP in that it does not exhibit strong coupling or ghosts up to cubic order in the interactions. We suggest that the nonlocal nature of the theory, when written in terms of the 4-D metric, is a plausible reason for this phenomenon. Finally, we briefly discuss the possible behavior of the model at higher-order in perturbation theory.