Soft Supersymmetry Breaking in Calabi-Yau Orientifolds with D-branes and Fluxes

TL;DR

This work constructs the 4D N=1 effective action for a stack of D3-branes in Type IIB Calabi-Yau orientifolds with background fluxes by dimensional reduction of the DBI and CS actions. The authors compute the full D3-brane Kähler potential and its couplings to bulk moduli, showing that the brane matter does not generally decouple from bulk fields and that flux-induced SUSY breaking is mediated to the visible sector via moduli F-terms. They demonstrate that for IASD fluxes soft terms appear with universal scalar masses and trilinear A-terms proportional to Yukawas, while ISD fluxes can yield vanishing soft terms or no-scale breaking, depending on the flux type. The results provide a controlled, general framework for flux-induced soft SUSY breaking in string-motivated brane worlds and highlight the Giudice-Masiero mechanism generating fermion masses in this context. The analysis remains valid for any CY orientifold with D3-branes and fluxes, illustrating how moduli mixing in the Kähler potential affects sequestering and low-energy phenomenology.

Abstract

In this paper we compute the N=1 effective low energy action for a stack of N space-time filling D3-branes in generic type IIB Calabi-Yau orientifolds with non-trivial background fluxes by reducing the Dirac-Born-Infeld and Chern-Simons actions. Specifically, we determine the Kahler potential for the excitations of the D-brane including their couplings to all bulk moduli fields. In the effective theory, N=1 supergravity is spontaneously broken by the presence of fluxes and we compute the induced soft supersymmetry breaking terms. We find an interesting structure in the resulting soft terms with generically universal soft scalar masses.