Red Density Perturbations and Inflationary Gravitational Waves

TL;DR

This paper analyzes how a red spectrum of primordial density perturbations influences the detectability of inflationary gravitational waves in upcoming cosmic microwave background experiments, highlighting the potential for detection across various models.

Contribution

It investigates the detectability of inflationary gravitational waves given recent density perturbation spectra, providing predictions for upcoming experiments and conditions for non-detection.

Findings

Planck can detect IGWs at >2σ for single-field inflation with V=0.

Cosmic Vision and Inflation Probe can detect IGWs at >5σ in surveyed models.

Certain inflation models could evade detection even by future missions.

Abstract

We study the implications of recent indications for a red spectrum of primordial density perturbations for the detection of inflationary gravitational waves (IGWs) with forthcoming cosmic microwave background experiments. We find that if inflation occurs with a single field with an inflaton potential minimized at V=0, then Planck will be able to detect IGWs at better than 2$\sigma$ confidence level, unless the inflaton potential is a power law with a very weak power. The proposed satellite missions of the Cosmic Vision and Inflation Probe programs will be able to detect IGWs from all the models we have surveyed at better than 5$\sigma$ confidence level. We provide an example of what is required if the IGW background is to remain undetected even by these latter experiments.