Aspects of Stability and Phenomenology in Type IIA Orientifolds with Intersecting D6-branes

TL;DR

This work comprehensively analyzes Type IIA orientifolds with intersecting D6-branes on toroidal and Z_N backgrounds, deriving precise R-R and NS-NS tadpole cancellation conditions via conformal field theory and boundary-state methods. It builds explicit, largely non-supersymmetric and supersymmetric models, including a stable three-generation Standard Model on a Z_3 orientifold and MSSM-like constructions on a Z_4 orientifold with fractional branes and brane recombination, along with detailed anomaly cancellation via generalized Green-Schwarz mechanisms. The study further investigates moduli stabilization and the potential for inflation within these setups, finding that closed-string moduli typically exhibit runaway behavior and that open-string moduli generally fail to support slow-roll inflation, though specific configurations at times allow partial stabilization or hybrid mechanisms. Overall, the work highlights both the promise and the obstacles of embedding realistic particle physics and early-un universe cosmology in intersecting-brane Type IIA frameworks, suggesting future exploration into higher-order orbifolds, gauge coupling unification, and robust moduli stabilization strategies.

Abstract

Intersecting branes have been the subject of string model building for several years. This work introduces in detail the toroidal and Z_N-orientifolds, where the main discussion employs the picture of intersecting D6-branes. The derivation of the R-R and NS-NS tadpole cancellation conditions in CFT is shown in detail. Various aspects of the massless spectrum are discussed, involving spacetime anomalies, the generalized Green-Schwarz mechanism and possible gauge breaking mechanisms. Both N=1 SUSY and non-SUSY approaches to low energy model building are treated. Firstly, the problem of complex structure instabilities in toroidal OmegaR-orientifolds is approached by a Z_3-orbifolded model, including a stable non-SUSY 3-generation standard-like model. It descends naturally from a flipped SU(5) GUT. Secondly, supersymmetric models on the Z_4-orbifold are discussed, involving exceptional 3-cycles and the explicit construction of fractional D-branes. A three generation Pati-Salam model that even can be broken down to a MSSM-like model is constructed as an example, involving non-flat and non-factorizable branes. Finally, the possibility that unstable closed and open string moduli could play the role of the inflaton is being explored. In the closed string sector, the slow-rolling requirement can only be fulfilled for very specific cases, where some moduli are frozen and a special choice of coordinates is taken. In the open string sector, inflation is not possible at all.

Figures (24)

• Figure 1: Splitting Interaction of a string compared to the corresponding field theory vertex, a coupling $g_{\mathrm{closed}}$ is assigned to this process.
• Figure 2: Perturbative expansion for the closed string partition function without insertion.
• Figure 3: A $Dp$-brane.
• Figure 4: Two exemplary branes $a$ and $b$ intersecting at angels on one $A$-torus with a topological intersection number $I_{a b}=3$.
• Figure 5: The two inequivalent $A$- and $B$-tori, corresponding to $b=0$ and $b=1/2$ in the flux picture.