Red Density Perturbations and Inflationary Gravitational Waves

Understand

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.