Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture

TL;DR

This work embeds tachyon-driven inflation within a KKLT-type flux-compactified Type IIB setup, leveraging warp factors to obtain suitably small slow-roll parameters and including the open-string completeness conjecture to constrain initial conditions. By dimensionally reducing the 10D action and constructing a comprehensive 4D effective theory with a single Kähler modulus, the authors analyze inflation driven by a non-BPS brane tachyon, show how warping and world-volume fluxes can yield sufficient e-folds, and provide explicit examples in KS throats and T^3 fibrations. They demonstrate that, in favorable geometries (notably large-volume, flux-supported T^3 fibrations), the model can achieve $N\sim 60$–$100$, produce a nearly scale-invariant spectrum with $n_s\approx 0.95$–$0.96$, and satisfy COBE normalization while keeping moduli stabilized. The results indicate a viable string cosmology path toward inflation with testable phenomenology, including potential correlations with cosmic string production and a controlled pre-inflation history tied to Sen’s conjecture.

Abstract

We consider a cosmological scenario within the KKLT framework for moduli stabilization in string theory. The universal open string tachyon of decaying non-BPS D-brane configurations is proposed to drive eternal topological inflation. Flux-induced `warping' can provide the small slow-roll parameters needed for successful inflation. Constraints on the parameter space leading to sufficient number of e-folds, exit from inflation, density perturbations and stabilization of the Kahler modulus are investigated. The conditions are difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3 fibrations and other generic Calabi-Yau manifolds. This requires large volume and magnetic fluxes on the D-brane. The end of inflation may or may not lead to cosmic strings depending on the original non-BPS configuration. A careful investigation of initial conditions leading to a phenomenologically viable model for inflation is carried out. The initial conditions are chosen on the basis of Sen's open string completeness conjecture. We find time symmetrical bounce solutions without initial singularities for k=1 FRW models which are correlated with an inflationary period. Singular big-bang/big-crunch solutions also exist but do not lead to inflation. There is an intriguing correlation between having an inflationary universe in 4 dimensions and 6 compact dimensions or a big-crunch singularity and decompactification.

Figures (6)

• Figure 1: The general setup for our model is IIB string theory compactified in a warped CY as shown here. The warped CY has a complicated structure with several throats in which the warping is big and several other parts where the warping is milder. The SM is placed generically in one of the throats, but its precise embedding is not specified (also, the fact that it is on a throat is not crucial for the model to work). There are a series of anti D3s placed on throats as in the KKLT setup. Inflation is produced by one or several non-BPS systems like D6s wrapping toroidal 3-cycles, D7s-anti D7s on top of each other wrapping general cycles or D8s in the middle of KS throats. Presence of electromagnetic flux on these systems is generic.
• Figure 2: Depiction of the CY as a $T^3$ fibration. (1) Locally, the CY can be seen as a $T^3$ fibration over ${\bf R}^3$. (2) The global structure of the CY can be very complicated but one can envisage that locally one can have D6 branes wrapped in the $T^3$ fibre at the point of maximum warping. Here $X^3$ represents the (3 dimensional) local base space.
• Figure 3: Effective potential with and without tachyon contributions. The thicker line shows the potential at the end of tachyon condensation while the thinner is the potential at the beginning.
• Figure 4: Number of e-folds vs $t$ and $a(t)$ vs $t$.
• Figure 5: $V(T)$ vs $t$.