D-branes in String Theories with spontaneously broken Super Symmetry

Abstract

In the context of String Theory, orbifold compactification has proven to be an effective method for breaking supersymmetry (SUSY) [1]. Specifically, freely acting orbifolds can be tied to spontaneous SUSY breaking, and the description on the closed string sector has been thoroughly studied [2]. This thesis aims to explore the effects of freely acting orbifold compactification in the open string spectrum. We first show that the orbifold compactification works as a projection on the spectrum of the non-orbifolded theory, where projection makes the spectrum invariant under the orbifold group action. Then, we link this result to a Scherk-Schwarz dimensional reduction that shifts the masses of all charged fields in accordance with the projected spec- trum. The main examples will be a D9-brane, for its simplicity, and the D1/D5 brane system. This system is closely linked to black hole solutions of the low energy supergravity, and in the last section we give predictions as to how the orbifold projection acts on the low energy worldvolume CFT and thus the black hole theormodynamics in the system with broken supersymmetry.