Tensor Modes in Pure Natural Inflation

TL;DR

This paper investigates tensor modes in pure natural inflation, revealing a natural lower bound on the tensor-to-scalar ratio due to Yang-Mills theory properties, with implications for future experiments and lattice calculations.

Contribution

It introduces a bound on tensor modes in pure natural inflation based on Yang-Mills theory, connecting cosmological predictions with gauge theory properties.

Findings

Tensor-to-scalar ratio r has a natural lower bound.

Future CMB experiments can test the model's predictions.

Lattice gauge theory can provide insights into vacuum energy dependence.

Abstract

We study tensor modes in pure natural inflation (arXiv:1706.08522), a recently-proposed inflationary model in which an axionic inflaton couples to pure Yang-Mills gauge fields. We find that the tensor-to-scalar ratio r is naturally bounded from below. This bound originates from the finiteness of the number of metastable branches of vacua in pure Yang-Mills theories. Details of the model can be probed by future cosmic microwave background experiments and improved lattice gauge theory calculations of the theta-angle dependence of the vacuum energy.