Smooth String Vacua in a Gravitationally Nonperturbative Regime

The strong coupling regime of four-dimensional <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>N</a:mi> <a:mo>=</a:mo> <a:mn>2</a:mn> </a:math> supersymmetric vacua of the heterotic string is analyzed from a dual domain wall perspective. Using modular invariance, we compute a closed form for the nonperturbative corrections to the supersymmetric domain wall equations, which enables a quantitative study of gravitational strong coupling regimes. A strong coupling singularity for the hidden Hořava-Witten 9-brane is resolved, and the domain wall interpolates between the visible 9-brane and a supersymmetric anti–de Sitter vacuum, thereby realizing a variant of the Randall-Sundrum model.