Constraints on Tensor to Scalar Ratio using WKB Approximation

TL;DR

This paper employs the WKB approximation to derive scalar and tensor power spectra, providing a method valid beyond slow-roll conditions and constraining the tensor-to-scalar ratio with results close to observational data.

Contribution

It introduces the use of WKB approximation for calculating power spectra and constrains the tensor-to-scalar ratio beyond slow-roll approximation.

Findings

Spectra are nearly scale-invariant and match observational data.

WKB approximation remains valid when slow-roll fails.

Constraints on tensor-to-scalar ratio r are obtained.

Abstract

Using Wenzel-Kramers-Brillouin (WKB) approximation the scalar and tensor power spectra are obtained. Scale invariant spectra are obtained and the spectral indices come very close to the observed data from WMAP and Planck experiments. The advantage of this method is that, it is valid even when slow-roll approximation fails. Constraints on the tensor to scalar ratio r is also studied with the WKB Approximation. We use the Power law inflation as the base model as it allows comparison with exact results.