Kahler Moduli Inflation
Joseph P. Conlon, Fernando Quevedo
TL;DR
This paper identifies a natural single-field inflationary direction among Kahler moduli in type IIB flux compactifications with $h^{2,1} > h^{1,1} > 2$ and exponentially large volumes. The inflaton is a small 4-cycle modulus whose potential is exponentially flat at fixed volume, yielding slow-roll inflation without fine-tuning and predicting $n \in [0.960,0.967]$ with negligible tensor modes and an inflation scale around $M_{inf} \sim 10^{13}$ GeV. COBE normalization fixes the stabilized volume to $\mathcal{V} \sim 10^5$–$10^7$ in string units, ensuring consistent density perturbations and a robust, model-independent spectral index. The mechanism leverages the no-scale structure, $\alpha'$ corrections, and nonperturbative superpotential terms, and remains robust against known corrections, while leaving open questions on reheating and initial conditions. This approach provides a concrete string-based large-field inflation model with testable predictions in upcoming observations.
Abstract
We show that under general conditions there is at least one natural inflationary direction for the Kahler moduli of type IIB flux compactifications. This requires a Calabi-Yau which has h^{2,1}>h^{1,1}>2 and for which the structure of the scalar potential is as in the recently found exponentially large volume compactifications. We also need - although these conditions may be relaxed - at least one Kahler modulus whose only non-vanishing triple-intersection is with itself and which appears by itself in the non-perturbative superpotential. Slow-roll inflation then occurs without a fine tuning of parameters, evading the eta problem of F-term inflation. In order to obtain COBE-normalised density perturbations, the stabilised volume of the Calabi-Yau must be O(10^5-10^7) in string units, and the inflationary scale M_{infl} ~ 10^{13} GeV. We find a robust model independent prediction for the spectral index of 1 - 2/N_e = 0.960 - 0.967, depending on the number of efoldings.