Inflation models selected by the swampland distance conjecture with the Lyth bound

TL;DR

This paper explores how the Swampland Distance Conjecture can impose theoretical upper bounds on primordial gravitational waves in large-field inflation models, providing a complementary and sometimes more restrictive criterion than observational data.

Contribution

It demonstrates that the Swampland Distance Conjecture can impose more stringent upper limits on inflationary parameters than current observations, offering a new theoretical tool for model selection.

Findings

Swampland Distance Conjecture constrains tensor-to-scalar ratio.

Theoretical bounds can surpass observational limits.

Provides a new criterion for inflation model viability.

Abstract

We investigate the extent to which the Swampland Conjecture can be employed to constrain large-field inflationary models from the perspective of quantum gravity consistency. In particular, we focus on the Swampland Distance Conjecture, which imposes an upper bound on the amplitude of primordial gravitational waves predicted by large-field inflation scenarios. This provides a striking contrast with the well-known Lyth bound, which yields a lower bound on the tensor-to-scalar ratio in such models. The two bounds thus play complementary roles in assessing the viability of inflationary scenarios. We demonstrate that, for certain representative large-field inflation models, the Swampland Distance Conjecture alone can impose more stringent upper limits on the tensor-toscalar ratio than current observational constraints from the cosmic microwave background. These findings highlight the utility of Swampland criteria as a theoretical discriminator among competing inflationary models, independent of empirical data.