Quantum Gravity Constraints on Inflation

TL;DR

This paper explores quantum gravity constraints on inflation, showing that entropy bounds limit certain inflationary models and large-rank gauge groups, impacting theories like racetrack inflation and KKLT.

Contribution

It introduces entropy-based criteria to constrain inflationary models, linking quantum gravity principles with cosmological model building.

Findings

TransPlanckian flat directions correlate with excessive inflationary entropy.

Entropy bounds exclude certain de Sitter models with large gauge groups.

Constraints challenge models like racetrack inflation and KKLT.

Abstract

We study quantum gravity constraints on inflationary model building. Our approach is based on requiring the entropy associated to a given inflationary model to be less than that of the de Sitter entropy. We give two prescriptions for determining the inflationary entropy, based on either `bits per unit area' or entanglement entropy. The existence of transPlanckian flat directions, necessary for large tensor modes in the CMB, correlates with an inflationary entropy greater than that allowed by de Sitter space. Independently these techniques also constrain or exclude de Sitter models with large-rank gauge groups and high UV cutoffs, such as racetrack inflation or the KKLT construction.