On String Vacua without Supersymmetry: brane dynamics, bubbles and holography

Abstract: In this thesis we investigate some aspects of the dramatic consequences of supersymmetry breaking on string vacua. In particular, we focus on the issue of vacuum stability in ten-dimensional string models with broken, or without, supersymmetry, whose perturbative spectra are free of tachyons. After formulating the models at stake in Chapter 2, we introduce their low-energy effective description in Chapter 3, presenting a number of vacuum solutions to the classical equations of motion. In Chapter 4 we analyze their classical stability, studying linearized field fluctuations, and in Chapter 5 we turn to the issue of quantum stability. In Chapter 6 we frame the resulting instabilities in terms of brane dynamics, examining brane interactions and back-reacted geometries. In Chapter 7 we propose a holographic correspondence connecting bulk instabilities with dual renormalization group flows, and we explore a potentially concrete scenario involving world-volume gauge theories. Finally, in Chapter 8 we turn to cosmology, deriving generalized no-go results for warped flux compactifications and concocting a brane-world scenario along the lines of a recent proposal, providing a string-theoretic embedding of constructions of this type. In Chapter 9 we provide a summary and collect some concluding remarks.