Moduli Vacuum Misalignment and Precise Predictions in String Inflation

TL;DR

This paper calculates how light moduli in string inflation models affect the number of e-foldings, leading to more accurate predictions of cosmological observables by considering post-inflationary evolution.

Contribution

It provides an exact computation of the shift in e-foldings caused by moduli vacuum misalignment in Kaehler moduli inflation, refining inflationary predictions.

Findings

Number of e-foldings reduced from 50 to 45 due to moduli effects

Spectral index modified at the percent level

Highlights importance of post-inflationary evolution in string inflation

Abstract

The predictions for all the cosmological observables of any inflationary model depend on the number of e-foldings which is sensitive to the post-inflationary history of the universe. In string models the generic presence of light moduli leads to a late-time period of matter domination which lowers the required number of e-foldings and, in turn, modifies the exact predictions of any inflationary model. In this paper we compute exactly the shift of the number of e-foldings in Kaehler moduli inflation which is determined by the magnitude of the moduli initial displacement caused by vacuum misalignment and the moduli decay rates. We find that the preferred number of e-foldings gets reduced from 50 to 45, causing a modification of the spectral index at the percent level. Our results illustrate the importance of understanding the full post-inflationary evolution of the universe in order to derive precise predictions in string inflation. To perform this task it is crucial to work in a setting where there is good control over moduli stabilisation.