Anisotropic evolution of 4-brane in a 6D generalized Randall-Sundrum model

We investigate a 6d generalized Randall-Sundrum brane world scenario with a bulk cosmological constant. It is shown that each stress-energy tensor $T_{ab}^{i}$ on the brane is similar to a constant vacuum energy. This is consistent with the Randall-Sundrum model in which each 3-brane Lagrangian separated out a constant vacuum energy. By adopting an anisotropic metric ansatz, we obtain the 5d Friedmann-Robertson-Walker field equations. At a little later period, the expansion of the universe is proportional to $t^{\frac{1}{2}}$ which is as similar as the period of the radiation-dominated. We also investigate the case with two $a(t)$ and two $b(t)$. In a large region of $t$, we obtain the 3d effective cosmological constant $\Lambda_{eff}=-2\Omega/3>0$ which is independent of the integral constant. Here the scale factor is exponential expansion which is consistent with our present observation of the universe. Our results demonstrate that it is possible to construct a model which solves the dark energy problem, meanwhile guaranteeing a positive brane tension.