Constraints on the spectral index for the inflation models in string landscape

TL;DR

This paper explores constraints on the spectral index in string landscape inflation models, suggesting that trans-Planckian field excursions are likely in the swampland, favoring a red spectrum with specific bounds.

Contribution

It provides a theoretical analysis of spectral index constraints in string landscape inflation models with sub-Planckian field variations, supporting the swampland conjecture.

Findings

Red primordial power spectrum with a lower bound on spectral index

Trans-Planckian excursions likely in the swampland

Tensor-scalar ratio and running are negligible

Abstract

We conjecture that the inflation models with trans-Planckian excursions in the field space should be in the swampland. We check this conjecture in a few examples and investigate the constraints on the spectral index for the slow-roll inflation model in string landscape where the variation of inflaton during the period of inflation is less than the Planck scale $M_p$. A red primordial power spectrum with a lower bound on the spectral index is preferred. Both the tensor-scalar ratio and the running can be ignored.