String-Inspired Higher-Curvature Terms and the Randall-Sundrum Scenario

TL;DR

This paper explores string-inspired higher-curvature corrections in the Randall-Sundrum model, showing that non-perturbative solutions with a Gauss-Bonnet term can produce consistent warped geometries and domain walls in five dimensions.

Contribution

It introduces a string-effective action with Gauss-Bonnet terms into the RS scenario, demonstrating non-perturbative solutions compatible with string amplitudes and analyzing their geometric properties.

Findings

Existence of RS-like solutions with string-inspired corrections.

Continuous interpolation between RS solutions and naked singularities.

Formation of domain walls restricting the bulk spacetime.

Abstract

We consider the O(a') string effective action, with Gauss-Bonnet curvature-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, with four-dimensional conformal factor Exp(-2 k|z|), can be a solution of the pertinent equations of motion. The parameter k is found proportional to the string coupling g_s and thus the solution appears to be non-perturbative. It is crucial that the Gauss-Bonnet combination has the right (positive in our conventions) sign, relative to the Einstein term, which is the case necessitated by compatibility with string (tree) amplitude computations. We study the general solution for the dilaton and metric functions, and thus 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 continuous interpolation between (part of) the RS solution at z=infinity and an (integrable) naked singularity at z=0. This implies the dynamical formation of domain walls (separated by an infinite distance), thus restricting the physical bulk space time to the positive z axis. Some brief comments on the possibility of fine-tuning the four-dimensional cosmological constant to zero are also presented.