Inflating in a Better Racetrack

TL;DR

This paper embeds racetrack inflation into a concrete type IIB string-compactification on IP^4_{[1,1,1,6,9]} with flux stabilization of the axion-dilaton and complex structure, leaving two Kahler moduli that are stabilized by a computed nonperturbative superpotential. A linear combination of the two Kahler-moduli axions serves as the inflaton, with inflation occurring from a saddle point and proceeding as eternal topological inflation; for a viable parameter range it delivers a COBE-normalized scalar spectrum at an inflation scale $M \approx 3\times 10^{14}$ GeV and a spectral index around $n_s \approx 0.95$. The analysis includes detailed slow-roll dynamics, the impact of noncanonical kinetic terms, and the sensitivity of $n_s$ to $W_0$, finding that anthropic considerations favor parameter choices yielding near-flat spectra. The work demonstrates that explicit string vacua with more than one Kahler modulus can realize racetrack-like inflation without adding branes and highlights the potential role of the moduli landscape and anthropic selection in determining observed perturbation spectra.

Abstract

We present a new version of our racetrack inflation scenario which, unlike our original proposal, is based on an explicit compactification of type IIB string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The axion-dilaton and all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler moduli are stabilized by a nonperturbative superpotential, which has been explicitly computed. For this model we identify situations for which a linear combination of the axionic parts of the two Kahler moduli acts as an inflaton. As in our previous scenario, inflation begins at a saddle point of the scalar potential and proceeds as an eternal topological inflation. For a certain range of inflationary parameters, we obtain the COBE-normalized spectrum of metric perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We discuss possible changes of parameters of our model and argue that anthropic considerations favor those parameters that lead to a nearly flat spectrum of inflationary perturbations, which in our case is characterized by the spectral index n_s = 0.95.