String-inspired higher-curvature terms and the Randall-Sundrum scenario - art. no. 124004

We consider the O(alpha') string effective action, with Gauss-Bonnet curvat ure-squared and fourth-order dilaton-derivative terms, which is derived by a matching procedure with string amplitudes in five space-time dimensions. We show that a non-factorizable metric of the Randall-Sundrum (RS) type, wi th a four-dimensional conformal factor e(-2k\z\), can be a solution of the pertinent equations of motion. The parameter k is found to be proportional to the string coupling g(s) and thus the solution appears to be non-perturb ative. It is crucial that the Gauss-Bonnet combination have the right (posi tive in our conventions) sign, relative to the Einstein term which is the c ase necessitated by compatibility with string (tree) amplitude computations . We study the general solution for the dilaton and metric functions, and t hus construct the appropriate phase-space diagram in the solution space. In the case of an anti-de Sitter bulk, we demonstrate that there exists a con tinuous interpolation between (part of) the RS solution at z = + infinity a nd an (integrable) naked singularity at z=0. This implies the dynamical for mation of domain walls (separated by an infinite distance), thus restrictin g the physical bulk space-time to the positive z axis. Some brief comments on the possibility of fine-tuning the four-dimensional cosmological constan t to zero are also presented.